Does an upgrade make sense?

I can't tell from looking at your system's photos, but you might want to re-address your set up to make sure you have optimized your system's potential. It looks like your speakers are on the 'long wall' and it looks like your speakers are a bit closer to the wall behind them. If possible in your room, set up on the short wall firing down the length of the room will give you a fuller sound, more pleasing to most folks. As presently set up now another foot out from the wall could give you a bit more sense of 'air' and depth (you have to adjust your listening chair as well). 

But if all that is moot, and you decide to go with some subs, consider whether or not you will use the subs with a crossover, or if you will drive your mains full range with the subs just additive in the lowest range. FWIW I hate crossovers.

FWIW, drill down your set up first. You can't really judge the contributions for a proposed DAC until you have that right (unless you want to build your entire system around a DAC, which sounds dumb to me). Re set up, ultimately what I would do if I had a room that size would be to drive the mains full range and set up two subs placed to smooth out the bass (usually where you are sitting) caused by nulls. If I wanted to fill the room with sound on the cheap, I'd just set up an old fashioned Hafler  system (using 2 separate satellites and a attenuator, and if you are semi anal about your main systems sound a seperate amp) There are so many trade offs.............:-)