Hi BC Dave;
A few years ago, I actually had a pair of Klipsch Synergy Series KSB 1.1 paired up with an older (late 90s) Klipsch center and quintets for rears. This worked quite well for small to mid-sized room with a larger percentage of movie related listening as opposed to music, but anything bigger (room-wise) would most likely yield the results you were getting w/the all quintet setup (audible compression, tinny sounding, etc.).
For the most part, assuming the speaker lines aren't vastly different (e.g., reference series vs. entry level series), speaker manufacturers tend to produce relatively similar timbre matching in their speakers, even models that are 3-5 years difference.
I would consider a pre-owned or new L/C/R set of Klipsch bookshelves and matching center, these three are the most important when it comes to timbre matching. In fact, Audioholics just finished up a bookshelf shoot-out that lauded the Klipsch RB-15s and considering their size, you'd have a better WAF, too.
Here's the link... -TD