The Solo Home was the center sold with the Concertino Home. It, unfortunately, in my opionion, was the weak link in the line. It's single mid-range just does not provide much punch. The Piccolo is a better choice, but, as you said, hard to find. I had Grand Piano Home's and ended up with a Thiel SCS3 (or 4) as a center. I now use that with my Cremona. To be fair, I never listed to the Solo with the Concertino as mains. My observations was the Solo with the Concerto Home and Grand Piano Home.
The Toy Center or the Venere Center may be an option, although I have not heard them. But they are also hard to find used. Given your requirements, the Solo may be OK, but I would be cautious. Although it is always best to use a center meant to go with the sides, in this case you may want to consider another brand.
The Toy Center or the Venere Center may be an option, although I have not heard them. But they are also hard to find used. Given your requirements, the Solo may be OK, but I would be cautious. Although it is always best to use a center meant to go with the sides, in this case you may want to consider another brand.