Need help improving my set-up (rig)

They are active speakers, so you aren't going to be able to drive them with an amp.

What soundcard output are you driving them with? It's possible that your soundcard's output is limited, but not likely. You could try switching between outputs (headphone output, line-out) or adding a pre-amp between the sound card and the speakers.

More likely, the speakers just don't have enough bass for your tastes. My suggestions, in order of preference, would be:

1. Try some equalization. Drop the treble gains and turn the volume up to get more bass-heavy sound.

2. Add a subwoofer to your setup.

3. Get some different speakers that have more bass.

The soundcard is fine, there studio monitors so there not designed to have booming bass just the bass thats in the track, you would be much better off spending that money on a sub to increase the bass extension.

Velodyne makes some really great subwoofers, also try Sunfire, HSU Research, or SVS

If you can find it within your budget, Wharfedale SW150 is another sub suggestion.

For your setup, make sure you get a sub with line-level L/R inputs. You can split the outputs of your sound card. One set goes to the speakers, the other set goes to the subwoofer.

Or, if your sound card has a dedicated subwoofer channel, you could use that.

For $200 look at the dayton range, you'd connect up via the subs unbalanced (rca) pass-thru you might need rca to ts cables I don't know how you currently have everything connected up and what outputs your soundcard has, a proper studio sub with a balanced xlr or trs pass thru like the krk 10s will cost alot more.