Are you using the Apple TV's analog outs? If so, a DAC will most likely improve things. I'm not very impressed with the Apple TV's analog outputs.
Make usre everything is ripped as either Apple Lossless or similar; no mp3.
What I've found in my system -
Synched music sounds better than streamed music.
Glass optical cables are better than plastic. I bought a $25 glass Sonicwave cable from Amazon and it sounds excellent.
The Audioquest NRG-1 power cable made a very good difference.
Make usre everything is ripped as either Apple Lossless or similar; no mp3.
What I've found in my system -
Synched music sounds better than streamed music.
Glass optical cables are better than plastic. I bought a $25 glass Sonicwave cable from Amazon and it sounds excellent.
The Audioquest NRG-1 power cable made a very good difference.