The reason I am asking is because I have a cs10 center channel and on the polk website they have the tsi 300's for that center.. but the monitor 70's are cheaper on newegg..
I can't recommend one over the other - but whichever way you go you want to have all three front speaker be of the same vintage to achieve timbre match. So either get the two tsi's or also get the center for the monitor 70s. (Lots of threads cover timbre match, so I won't bother regurgitating here.)