I agre with Ryder. The Solo Home center is very musical and does well for voices. Just not very punchy. The series before the Home series was bi-wireable so I assume that the center on e-bay (which it says is bi-wireable) is part of that series. I have not seen it before. It might make a good match with the GP. I have a pair on Concertino Home and a pair of the original bi-wireable Concertino. The sound is pretty similar although the bi-wireable one is somewhat less efficient. Many like the bi-wireable series better than the Home series. My concern is that SF is noted for this musical nature but did not really design for home theater. So, the center may be musical, but not punchy enough for a center. They paid more attention to home theater with the Domus series I think.
The Cremona are in a completely different league than the GP. However, they are somewhat picky about electronics and cables so to get the best from them means additional investment in preamp, amp, cables and probably sources. I ended up building up a new system for them - Classe pre, Levinson amp, Classe CD player, Transparent cables - which cost more than the speakers. For music it is really awesome. For movies it is overkill. FYI - I do not like the new Cremona M compared to the original Cremona. Starting with Domus I think they went away from their musical heritage and went to a more detailed sound that, for me, is much less enjoyable than the Guarneri, Cremona, Amati, Stradivari type sound.