i have the Sigma SSPAmp 5 combo powering my new 802 d3s, HTM2 d2 center, and 805 d2 surrounds (also DB-1 sub). it gives a beautiful neutral, detailed, yet full-bodied sound. I haven't detected any strain at all in powering the 802 d3, which recently replaced 803d2's I had for about 8 months. I am still breaking in the 802d3s, but I do wonder, while the low end I get with the Amp 5 powering them is well controlled, whether I would get more weight and dynamics using a more powerful/traditional amp such as the 2300. I heard the 802's at Magnolia powered by MacIntosh 452 and I heard quite a bit more weight (although those speakers were no doubt broken in).
I compared this setup to the Nad M-series Class D combo and, while both are excellent, I felt the Classe sounded more neutral (Nad was a little darker and slightly grainy). I hear no graininess in the Sigma (one of the design goals of this series). The Sigma amp is perhaps missing a bit of dynamic punch and low weight typically heard by high-powered conventional amps, and may not have quite the air and high frequency extension I've heard (I've owned a CA-201 and CAV-75 setup with SSP-20 in the past for comparison, as well as demoed a higher power Emotiva amp), but these differences are really pretty small. The overall sound is smooth and refined, and while I hope some day to give the 802s more power, I can't really complain with the sound I'm getting
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The features included with the SSP are quite comprehensive unless you're looking for room correction (although there is a way to fine tune frequency response, just no included software to do it automatically). I tried Emotiva's room correction setup/software and found the software colored the sound in an undesirable way (yes, the DIRAC that everyone raves about). I didn't really care for it...while the software can make the soundfield more cohesive and even out bass response, I found the SSP's preamp/processing sounded better, and my DB-1 came with its own software to smooth out the bass.