As Jaybo so succinctly stated, when making your first venture into SET-land, start with your speakers and they will dictate your amp choices.
BTW, "flea power" to most people means anything under 20wpc, but to SET fanatics, that usually means 2wpc or less - the lunatic fringe. (joke)
One thing you have working for you is a (relatively) moderate sized room. Getting tight deep bass will be much easier with decent-sized hi-eff speakers.
do you C&C subs work well with your speakers?
Yes, but my room was nearly twice the volume of yours and opened on one side down onto my dining room of equal size. The advantage of two subwoofers is that they tend to cancel out a lot of problems caused by a single sub, though setup can be a bear to get right.
When you say I need to spend a lot of money, how much are you talking about?
Shindo makes really high quality components, getting amps and speakers of equal performance/quality will cost you, or, take some serious homework and patience to achieve at a lower cost.
Also, "Slam" is something that SET systems don't do particularly well at any cost. Getting bass equal or similar to what you are used to with the Gerschwins will not be easy. SET is a system of tradeoffs, a little less bass production can get you a lot more of everything else, musically.
Audio Note, Omega, and Zu are great speakers, but there is no way you will ever get the same level of bass output as your Gerschwins with higher powered amps without far larger cabinets(excluding Zu's Definitions which have built-in bass amps/subwoofers). We are talking about smaller drivers and/or smaller cabinets with less power, simply no way.
So, I really, really, suggest that you look into hi-eff speakers before buying an amp. See what the benefits and limitations are first. Decide on a size appropriate for your room and musical tastes, then look for amps. Otherwise, you may end up unable to drive your speakers well enough to satisfy your musical needs.
Once you get that settled, there is quite a large selection of high quality SET amps we can help guide you through.