I would abstain from taking it with you at all. It is a lot of trouble, and a lot of risk. Sending it with a parcel service is almost certainly the better choice.

I don’t live in the USA, but I’ll just assume rates are not that much different. Sending a parcel of that size and weight to Turkey with a well-respected three-letter-acronym parcel service would cost me 35€, plus another 25€ to have a 2,000€ (~$2,200) cover-all insurance.

You have to consider the following:

• There is a limit on how much weight you are allowed on your suitcase, usually something in the low 20s of kilograms. I don’t know about you, but I am almost always pretty close to that limit, without carrying 8 kilograms of audio equipment. Overweight is excessively, prohibitively expensive.
• Carrying around the valuable equipment and worrying what may happen to it makes the trip a no-fun experience. You know, you could get stolen/robbed on your way from the airport, too. The trip by and in itself, plus the time shift is already stressful enough, isn’t it?
• Your suitcase can be, and will be opened without leaving a trace by at least the TSA, and possibly by someone handling luggage (who isn’t entitled to do so, but can do anyway, the keys are easy to get, every criminal has them).
• The chance of the postman running off with your equipment is none greater than it being stolen or damaged at the airport. In fact, in my personal experience, it is smaller. I’ve had one suitcase “disappear”, two lost and found again, two sent to a wrong destination and delivered two days later, one broken, and one literally destroyed with tyre tracks on it during the last 30 years. I’ve had zero parcels damaged or not delivered.
• Even if you get one of the “not catastrophic” failures, such as your suitcase going to a different destination and being delivered two days later, it’s immensely stressful for you to not know what’s going on, or if you will ever see your suitcase again. Parcel can be tracked online at any time, if you ever wonder that it should already have arrived.
• There is that thing about customs, too. You said “It’s their property, legit”, but you had better have good evidence for that claim (and documents proving the stuff was previously exported, or properly taxed). Otherwise, when the customs officer yells “You, open suitcase” at you, it becomes unpleasant. Being arrested for smuggling is no fun, but in particular not in Turkey. Generally, dealing with officials can be very much no-fun in Turkey at the present time.
  It is of course a bit of the the same situation when receiving a parcel from abroad — it will be seized by customs and you have to fetch it from the central repository. However, there are two important differences. First, you cannot be arrested (well, OK… you can always be… even for no reason at all) because you didn’t carry the goods over the border, you are just claiming a parcel that someone sent. The absolutely worst thing to happen — normally — is the parcel being confiscated, or you have to pay a customs fee or, uh… bribe. Second, and more importantly, you will have your friend who is a native speaker living in that place with you. Which is an immensely different, less malignant, situation compared to being stopped at customs with your suitcase in your hand.

One thing I have often heard suggested is to put a single bullet in the check-in baggage, and this will cause them to treat the baggage with extra very-strict security. There are a lot of personal testimonies online from photographers, musicians, etc. who have used this method.

http://lifehacker.com/5448014/pack-a-gun-to-protect-valuables-from-airline-theft-or-loss

Airlines sell extra valuation insurance or other forms of insurance that include extra baggage protection. The details vary from one airline to another, so I can’t give you a firm answer. Besides the total amount ($2000 is not going to be a problem) you have to make sure that electronics are included. Turkish Airlines. The baggage limit appears to be 3500 Euro.

The general life advice

Can’t afford to lose it?

Insure it.

https://www.allianzmusicalinsurance.co.uk/

Either Travel insurance that covers up to the value in luggage (check for single item limits and excluded items), or insurance for that specific item wherever it is, or some kind of shipping insurance for the specific journey. All these products are available, you just need to see which works best to you.

The (probably more expensive) alternative

Many airlines allow you to buy a seat for certain classes of large items (like musical instruments), so that you can take it on the flight with you. Now, a flight from the US to Turkey is likely to cost a lot more than insuring a mere $2000 item, but at least this way you can be pretty confident that if you make it all the way there, then it will.

Note that the procedures for how to do this, and what items are acceptable, vary from airline to airline. Either check your carrier’s rules and advice online, or give them a call.

The other thing you may want to know

Side note – if this item is remaining in Turkey, you’re almost certainly legally required to declare it to Turkish customs. How much it would cost, or how likely you are to be caught if you don’t declare would be beyond the scope of this answer.

If you want to put it into a luggage, you’ll need to buy an extra large luggage.

There are also specific boxes set for this kind of items :
https://www.amazon.com/s/ref=nb_sb_noss_2?url=node%3D11974841&field-keywords=road+case (search for road case or flight case)

Then, I would strongly suggest you to buy an extra insurance specifically for this item. The likeliness of a theft is limited as it is a big item and it is easier for robbers to stealth small items. So most likely, they won’t bother with this. Then it might get damaged, this is the biggest risk. To prevent this, protect it properly 🙂

Tell them at the check in that something is super fragile and needs to go into special baggage. It’s usually a seperate desk away from the standard checkin desks.

Theft shouldn’t be any more of an issue than usual. Istanbul is a major international airport, you’re not flying to some little countryside landing strip out in the middle of the 3rd world. When you pack it up like hell just make sure it looks like nothing valuable. I’ve observed that its pretty common for middle eastern travelers to often check in mysterious boxes and Istanbul will be used to a lot of these passing through.

I’ve never went with anything costing $2000 though I have flew with a TV before. It went without problems.