Hey charan,
First, thanks for your kind words regarding my reviews. With out copping out, both are great amplifiers with slight differences. The SPL S1200 has an overall smidgen of warmth (velvety) while the S5.5 is more neutral and has what I describe as a (silky) overall presentation. Both have great top ends. However, the shimmer/details of the Coda S5.5’s high frequencies is still something very special compared to any solid state amp I have tried. If you have speakers that can get a bit bright/forward sounding the S5.5 might not be a great match-up. Both are great at producing large sound-stages. Each is very musical and the antithesis of being analytical. Regarding overall speed, dynamics, bass control, and a sense of aliveness both amps are reference level. If you love your SPL S800 you would really dig the S1200, keeps the mid-range magic and adds on to it. (If you read my review on the S1200 it gives the details of these wonderful additions.) If you want a slightly different "flavor" the Coda S5.5 would provide that in your system. By the way the S5.5 matches great with the SPL Elector preamp.
I love to use tube analogies to describe the sonic differences between pieces of equipment. For my ears the S1200 is slightly towards the warmth of a great 300B or E-34 tube, while the S5.5 is slightly towards a great 2A3 or 211 tube. These are exaggerations, but give a taste of the differences that people can relate to if they have heard the different tube "flavors". So, it really does come down to personal taste and system synergy.
Teajay (Terry London)