Rademaker,
your question is a loaded one! ;-)
The Apogee Scintilla comes in 2 flavours - one, a 1-Ohm only version & two, in a dual/user settable 4-Ohm & 1-Ohm version.
The 1-Ohm version sounds much better than the 4/1-Ohm version but is incredibly hard to drive! The 1-Ohm version Scintilla drops to 0.93-Ohms in the bass region (can't remember if it the bass or mid-bass region). So, you WILL NEED an amp that is stable down to 0.5-Ohms. AND, you will need an amp that is ATLEAST 1000W/ch into 1-Ohm. There are very few such amps (count on 1 hand) & these amps are going to cost you BIG MONEY! Further, you will be restricted to s.s. only amps. This you might or might not like - I don't know your preferences.
So, the getting an 1-Ohm Scintilla has a large cost when it comes to TOTAL cost of ownership.
The 4/1-Ohm Scintilla is much easier to drive & you can use tube amps as well. Of course, not any tube amp but several of the "fortified" power supply ones (I'm thinking atleast 100W/ch with a large power supply). You will need a large output wattage tube amp to bring the best out of this speaker as they are quite power-hungry. They are also terribly inefficient: 79dB SPL at 3m per the user manual.
Over & above all of this, you are likely to find an used speaker that will need refurbishing (not cheap!) unless you are lucky to find one that has already been refurbished (which is likely to have a fairly high selling price).
I hope that someone w/ a 4/1-Ohm Scintilla comes forward to share his/her experience re. to these speakers. I personally have the 1-Ohm Scintilla (& I like it very much).
Never heard an Infinity Renaissance 90, so no comments.