OK all i set up my 6C new. and my 6T's @  80hz's as THX request.. Bought a decible meter from radio shack annd calibrated all to within 3 decibles.

 Is that ok or am i missing something. All sounds great to these 50 year old ears... lol

My Denon set up my 6 T's at large at first' And i had a smaller Canton center. Now in the first week of the 6 C and yes its bigger and less timbre as a canton. But some music is very tinny?

I think they sound best when set to large or full band.

I'd try both along with 60 for an in between alternative and let your ears be your guide. 
 

gregrry, I have a little more to add to either your confusion or fun (depending on your perspective).  I too have the 6Ts and 6C, but my receiver only offers a global crossover setting (meaning I can't set a different crossover frequency for different channels).  Because of that, I set all of my speakers to "small" and go with the THX recommended 80Hz crossover for when I watch movies.  But when I listen to music, I change my receiver's subwoofer settings to output to "both" the front speakers and the subwoofer (and this automatically defeats the 80Hz crossover for my fronts).  I have a huge room and I like lots of bass, so I found this gives me better result for music (I should note that I do not listen to multi-channel music).

If your receiver has a global crossover setting, an alternative to what Jason suggests is to set your crossover to the weakest link in your speaker chain in terms of low frequency output.  For example, your 6Ts are rated to go down to 36Hz, your 6C is rated to 55Hz, but if your surrounds are rated to say 65Hz, you could try a crossover setting of 70Hz and see how it sounds.  Good luck, have fun, and enjoy the sound- that's what it's all about.

-Nick

I think this is going to be a good discussion. 

I have a bit of a different setup. For audio I use an older receiver (130wpc) without a sub for my 6T's so they are "full spectrum." I really like how they sound for this. For movies I use my onkyo 805 (130wpc) with them set to 60hz along with my 6C. They sound great for musical DVDs but engaging the 8D for the lower frequencies really gives the low notes a kick. For example on movies with large booms I much prefer the 8D. Now we can discuss how the two receivers are different and that audio through the older receiver is inherently different because the onkyo internally decodes while the oppo dvd player decodes CD's for the older receiver....etc but I am only trying to make the point that the 6T's for music sound best when set to large and for movies using a sub really gives it a kick.

I'm not sure about the denon but with the 805 when I set my fronts to large it asks if I want to double to bass with the sub. I tried it and didn't like it because I felt the low frequencies echoed and it wasn't "tight." I may not have played with it enough since Nick doesn't seem to have the same problem.

I listen to most of my music as 2 channel but when I've played with the onkyo's all stereo thing I thing the 6C sounds equally deep as the 6T's with the 60hz cutoff. If yours is new, maybe give it a chance to open up a bit.   

Just my 2 cents.  

-J