Would adding a Dac improve the sound for my setup?

Musical Fidelity V-DAC for $299. You can return it if you don't hear a big difference; I think you will. Use a decent digital cable.

Well, my $300 DAC operates in the company of Gamut L5s [$15000 retail] CJ 350 [$10500] Audia line stage [$7000] and 2 REL subs [$6000] and holds its own quite well. Is it the best DAC available, of course not; but HIFICRITIC said that they had never tested an active component at this price level that could be used in high level systems like the V-DAC. With an external power supply it is even better. It is just too cheap for most ; it took a friend almost 2 years to convince himself to get one. He is very happy with it.

My wife liked my Ready Acoustic panels so well she made me buy some more when I moved them to another system. YMMV.