You'll be fine with an XPA-3 over the XPA-5. Save the cash.
Mine are set to "unbalanced" (running RCA interconnects), as the amp is about a foot from the pre-outs.
The speakers sound fantastic, and your 6T's will definitely benefit from the extra power vs your Denon.
Emotiva has a similar return policy to Aperion. All the advice from myself or others will not do your own ears any good. You'll have to just listen to your speakers, in your room, yourself, to really know. I'd say get it and if you don't feel the purchase is warranted, it should be easy to send it back.