looking for a DAC that will add some bottom end

If you want not only deep base but 'articulate' base, get a PS Audio DL3 with a Cullen Circuits mod. It not only resolves lower frequencies better than the stock, it also opens the air around the bottom end better. You'll hear the wood of the kick drum instead of a dull thud. You'll hear the resonance of the strings on the base instead of a simple low pitch rumble.

It runs you about $1,500 new. While it is more than you want to spend, you won't find equivalent bottom end performance for under $2,000.

The bass is incredible on the Cullen. Not only is it deep and strong, but it also does exactly what Shazam above says. It articulates the bass, opening it up and resolving all the resonance, the wood sounds of the doublebass or the drums. Not a thud that just dies, but a sound that rings and resonates and sounds like the real thing. It's hard to give this up once you experience it.