Picked up a set of mm651's, will one single soundstream 4.520 handle 2 tsd6902r's the polks and the titan xl's or will the 3ohm nature of the polks throw it off?

 

how are you planning to hook up?
titans and polks together on Front out of amp and Pioneers on the back?

SS is 2 ohm stable...

as you know titans are 4 ohm
polks 2.7
pioneers 4

polks together with titans or pioneers will drop the impedance below 2 ohm(1.61194029851 !!!)
not sure if I would do that / if it it save (not a huge drop on the impedance but it does go below minimum) ... leaving to the real experts (UN/GP/Pioneer74/...) to comment on this...

you probably saver to parallel the titans and pioneers (resulting in 2 ohm) and run polks alone. you can always fade the sound to either "set" through HU.
I run +4 to the pioneers.

go to:
http://www.speakerimpedance.co.uk
and look for parallel calculator - instantly gives you the impedance and Power to each speaker...

 

I'd hate to divide the wattage in half going to the Pioneers !