Try Standard Audio in Ocean Terminal, TST.
The man to speak to is Kenneth. I was put onto him by an FO I flew with, and I always go directly to him. I know a number of CX pilots who use him.
Same as in the thread above, don't go for window shopping, although I've found him very knowledgeable, and will give honest suggestions/recommendations about the choices available.
Their prices for regulars & referrals (ie potential regulars) are usually excellent, and there is no "negotiating" necessary - they quote a price, and that's your price.
Most importantly, when he quotes the tech specs on a product, I know I'm getting the truth, not a beefed-up sales pitch.