>Denon avr 2105 For now, will upgrade later.
I'd recommend that your receiver upgrade be instead an external amp for your fronts that the 2105 plugs into, and that you look into rti8, rti10, or rti12 fronts instead of the rti6.
I have rti4 surrounds, and do like them alot, but I recently got rti12's for the fronts, and use a Denon 3805 with an external pro-amp (rated 400 watts per channel), and the sound from the rti12's blows away the rti4's. I would assume it would blow away the rti6's as well. I'm not talking volume, I'm talking clarity, crisp sound, front imaging, the whole thing...
After hearing properly powered rti12's, I would never get the rti6 for my fronts unless severely budget constrained. If that was the case, I'm sure they will sound "good" based on my rti4's, but not as good as the biggies.
I'd also look into HSU, SVS subs for around $400. And while you're at it, look into the Mirage S-12 sub sale at vanns. I got the S-12, and it is incredible with my polk system. For the price, consensus seesm to be that at the < $500 price point, HSU, SVS, or the Mirage are the best game in town, by a VERY big margin.
Thinking about amps, with the csi5 and the 2105- could the 2105 have any trouble powering it? Just a thought.