First, great preamp - I am a big fan of the MFA Lumi and Magus preamps. As to your question, I had entry level Magnepans back when I was in law school (almost 20 years ago, now), and experimented with a number of solid state amps at the time. I don't think solid state amps are "inherently" better with the baby Magnepans; rather, you simply need an amp that can deal with their relatively low sensitivity (as I recall, the MMGs are ~83db/2.83V/m), which does require an amp with some juice behind it.
As to the KSA100s, I would recommend you try before you buy, as the combination does not seem to me to be the best fit. If you are wedded to the KSA series, I would actually recommend you consider the KSA-50s, which had the sweetest treble and the best overall balance of the line (from my recollection). As to other solid state amps, I had good success with Jeff Rowland amps - you can get a pair of Model 3s under $2k, and I think they would make a nice combo with the Maggies. Also, the Plinius SA-50 (mk ii or later) or SA-100 would be solid choices. For amps of more recent vintage, the Odyssey Kismet is a nice amp, and can probably be found under $2k used.
One caveat, however: I am not sure of the output impedance of the MFA, but suspect it is on the higher side (you might want to check with Scott Frankland, who is the "F" of MFA). As a result, you need an amp with a higher input impedance. The Plinius amps had 100kOhm input impedances, and the Rowland Model 3 had a selectable input impedance with 100kOhm as the maximum, of which should work well. Other solid state amps may be much lower, which could present problems with the MFA. (If you are wondering, the Krell KSAs were 47kOhms, which should also be OK).
With all that said, if it were my upgrade $, for the $2k I would go higher higher in the Maggie line, grab a pair of 3.6Rs and not think twice about it (two of these are on the 'gon right now for ~$2k) - they will give you much better bass extension and better dynamics than the MMGs, thereby potentially solving your issue.
Best of luck.