Thanks a lot for your response Gonk.
First your point regarding the volume is very valid. I never thought of that. Adjusting the volume on an HTPC is not that practical, because you need a mouse nearby, and to come back to the window etc...But my case (crown CW02 from silverstone: tip: absolutely brilliant case, allows you to build a monster PC, yet totally silent because it has room for the right components) has a volume button, and a remote. It never occurred to me I would use it, but if I remove the Yam, then I will.
One good news is that you seem to think the 7125 would be good enough (I don't push anything to the max anyway), so the budget becomes very reasonable indeed.
Since I'm no expert, I can't make my mind on this power thing. It seems there's a consensus that the Yam & others' rating like 7*110 W is greatly exaggerated, compared to "all channels driven" ratings.
But then it comes down to an apparently very debated topic: the higher amp Wattage above speakers W the better? equal is fine? if amp is lower there's a risk of blowing the tweeter, is that an issue for common people? etc.. not forgetting what I read quite often: a powerful amp will get the speakers to "speak" at their upmost quality even at low volume...
So going for a dedicated power amp, is that only a question of power, or also a question of quality? I must admit that, not being in electronics, for me once the signal is generated (by the sound card in that case), that's it, an amp will not remove some voices or some crashes, or put a horn where there is none. But that may be where I'm completely wrong and overly incredulous about putting money in a separate amp.
Could you convince me a bit more?