They are both good components.
Specifically the Pioneer elite 55TXi and the 56TXi vs. the Yamaha v2500. In terms of sound clarity, open soundstage.
That would depend on your speakers, room acoustics and the recording quality.
I am mainly concerned about sound quality. I read that the Pioneer elite receivers use MOSFET amps, so that should give them a warm, smooth sound.
No, not at all. It depends on the design quality and is reflected by the specs.
But, both components will give you transparent sound out of the amps. Again, speakers, room acoustics and recording quality that matters.