Hello jmilliz and thanks for your inquiry. Timbre matching simply means that the speakers have a similar tonal balance and sonic signature so that when the sounds move from one speaker to another it's seamless and natural. All of our speakers are actually timbre matched to each other and across the series, so the 6Ts with the 5C will work perfectly and sound great together. Subs don't really have much in the way of timbre since they're all low frequencies, but our subs are all designed to blend seamlessly with our speakers as well.
Hope this helps, and happy listening.
- Oliver
Oliver Amnuayphol
Home Theater/Audio Guru
Aperion Audio