I own a pair of Ren 90's, and I love them, they are GREAT speakers !! However, I dont think they are really all that power hungry as some people think they are. (Certainly not like the notorious Kappa 9's :)
I am a vintage Sansui enthusiast and I own a whole bunch of Sansui amps & receivers. I have used my Ren 90's with my Sansui BA-5000 (classic 300 Watt amp made in 1975-1977, I own 3 of them, actually), but I have also used my Ren 90's with as "little" as a 60 Watt Sansui 7070 receiver (and 60W Sansui G-5500) and the speakers sound fine.
Its up to you if you want to spend big bucks on moderm hi fi equipment such as the latest amplifiers that appear in 'Stereophile' mag and the like, (and I did once own an Odyssey Stratos myself) but I think you can just check Ebay and get yourself a really nice vintage 1970's amp- back in the day when things were built with real quality, no cheap black plastic junk.
By the way, on the Yahoo site there is a Message Board for Infinity enthusiasts. Simply select the 'Groups' link on the Yahoo homepage, and join the 'Infinity Classics' Group.
I hope you will enjoy your Ren 90's, as I said before, they are FANTASTIC speakers! Just curious, where did you buy them? Do you have them in blonde oak (which is what I have) or black ash? I'm not that keen on black ash, but there was a limited edition hi gloss black lacquer which look absolutely stunning, (very rarely seen for sale anywhere Online).