Subwoofer - is there one that would work in this situation?

My main speakers are the Janzsen Valentina P8s, which I love, they just lack a little low end punch. I'm thinking about adding a subwoofer but the only place I have for one is on the bottom shelf of the built in shelves below my TV.

Questions:

Given the location limitation is there a subwoofer that would work? 

If so, Im thinking a small forward facing sub with DSP. Suggestions?

Thanks in advance....