Absolutely, you may use an XPA-2 Emotiva amp with our speakers without voiding the warranty. There's nothing in our warranty literature that precludes you from using any amp or receiver with our speakers.
However, blown drivers due to either under or overpowering our speakers are not covered under the 10 year limited warranty. We will still repair the speaker for you, but will likely charge you for the replacement parts.
But I would say that it would be pretty difficult to blow out the 6Ts with that amp, so I wouldn't worry about it.