Wow, a blast from the past, I had Alon IV's many, many years ago, purchased them from Arnie, founder of Audiogon. I modded those things to nth degree, went to the Alnico magnets, modded baffles and bass box. Later on went to the Lotus SE when I went to tube amps.
No way do you need 500wpc with the IV's, I ran them with NAD amps, then NEW (Nirvana Electronic Works) DCA 66, 60WPC Class A battery powered, then Conrad Johnson MV55, at which point I changed to Lotus.
I have no idea of 'strain' you're hearing, certainly not lack of power! And going to more efficient speakers will likely exasperate issue. You've got to match speakers to amp, I've found Alons like tubes for mids and tweeter, however, need a modicum of amp damping factor to get bass right.
You're problem may be elsewhere in system as well, strain and lack of resolution can be result of many things.
As for future speakers, could never get used to box speakers after open baffle Alons. Now have modded Klipschorns, give me everything Alons did and so much more!