Subwoofer Advice For Stereo Music System, Not HT

I recently purchased new the following:

Jolida JD302BRC Tube Integrated Amp
Jolida JD100 Tube CDP
APC H-10 Power Conditioner
Wireworld Cables and Interconnects

all added to my current Klipsch KG5.5 floorstanding speakers.

I absolutely love the mids and highs produced by this system, but the lowest frequencies, while nicely detailed, are just not quite balanced with the mids and highs. I have had the system for a month now, and have at least 40 or 50 hours on the system. I have tried numerous speaker placement options, and currently have the speakers placed almost against the back wall. This gives the best bass, but still not quite what I seek. I have decided I may have to add an active subwoofer. I can't help but believe that the proper sub would be the final piece to make this system really shine for my small 13x14 listening room. The system is used only for music, no home theater.

Given the above, what do you think I should I look for in a sub? I am currently looking at the Velodyne MiniVee or the Velodyne SPL-800R. I would think these models should give me the added bass while keeping distortion and boominess to a minimum. They are also sealed instead of ported, which I have read is better for stereo music. Am I on the right track here, or are there other models/brands I should consider? My budget is $1k or less.

Also, the Jolida int amp has two sets of pre-outs. One fixed and one variable. Which would be more beneficial to use for the sub, or should I just hook the sub to the speaker binding posts?

Thanks.