Sadly, you are not going to find anything to match the sound quality of your current set. Flat panel TV's all seem to have much weaker sound than the bigger projection based TVs had.
LCD:
Vizio has a 55" 1080p LED LCD coming out within the next couple of months that should be pretty nice and will have an MSRP of 1999. Their current 55" can be found around 1600 or so and does not have the local dimming LED backlight.
Toshiba has the 55ZV650 which has been getting quite good reviews and can be found for under 2000. The Cnet review of the 47 seemed to only really critique the black levels, but the 55" screen uses a better panel than the 47" does. Their LED 55 coming out will be about 2600 MSRP and might be found for near 2K but it will take a while for sure.
Samsung's cheapest 55" is the 55B640 which seems to be from Best Buy only and well out of your price range. The 55B650 is even pricier as well. Beyond that the Luxia 55" sets are up in the 3K range if you are lucky but I doubt you are concerned with the thinness the LED sidelit luxias provide. While I love Samsung TV's I think their 55" TV's are currently all priced out of reality and they definitely need to come down.
Plasma:
Panasonic has several 54" Plasmas coming out quite soon. Depending how bright your room is these should perform pretty well. You might also be able to find a 58" Panny plasma in your price range if you are lucky. Panny probably will have the best sound of the bunch as well.
Another plasma option is the 58B550 from Samsung, which you can easily find for 2K and is known for having very accurate colors. The B series plasmas seem to be much improved over last years A series.