Hi Expat and a very warm welcome to Thailand!
I can't believe you came to Thailand in the middle of our chaos, good on you.
Well, regarding your search, I would suggest you visit Siam Paragon. On the 2nd floor near luxury car dealers, there are plenty of Hi Fi shops sitting side by side.
Another one of well-known Hi Fi shops in Thailand is called Piyanas, where you check out their site online which shows all their products with prices. They also have many shops around BKK where you can go for a demo.
There are also many online sellers who sell some brands that you may not be able to find in the shop in BKK and usually the price is cheaper, depending what you are looking for.
If there's anything more I can help, please let me know. Hope you have a wonderful time here