Pay cash!
Credit cards only add more to the price tag.
lol
I gave this a lot of thought a few years back. Primarily because I wanted more out of what I had than I was getting then. My issue was more a 'desired difference' in the sound itself than in the area of proper power applications.
I found my answer or an acceptable one by changing both speakers and amps... and another amp or set of speakers might yet be forthcoming. Though I'm in no hurry, so that says something too I suspect.
Although if one is plumb serious and dedicated to the propositio of bi amping, great results can be had, I think the majority of the crowd here will opt for more closely matching amps to speakers... or vice versa than to add more amps to the existing speakers given the possible pit falls pursuiant to that matching.
I suppose though it ought to be enlightening, and perhaps fun too just to see what happens.
I'd think a set of active lower end speakers whose only needs were those for powering the mid & Tweeters might be where I'd go. Maybe. Good luck in any event.