If you used a 1/8" to RCA convertor cable to connect the TV to the Audio-GD DAC, you could be losing sound quality because of poor cable as well as poor audio from the TV. If this is the only way you can do this, then there's nothing much you can do.
I always advise using digital COAX or toslink cable to connect to the DAC.
As far as bass, the Yamaha studio monitors are pretty good on the bass, as long as your source is good (see first paragraph). If you feel you are missing bass, it is most likely an acoustic problem with the room. I have been there. Room probably requires bass traps to reduce the standing waves.