Powering Old Infinity towers with Peachtree 125 sky-- with analog EQ

I'm guessing you are talking about vintage Infinity RSIIIs? RS-3s, not RS 111 (one hundred and eleven)?

Check with the gang over on the vintage Infinity speaker forum on AudioKarma:

https://www.audiokarma.org/forums/index.php?forums/infinity-loudspeakers.129/

Also, to look up specifications, try:

http://www.infinity-classics.de/

It's in German language, but you can usually poke around and find what you need.

Here is a suggestion: Fix the room, not the electronics.  And if that doesn't cut it, from what I read, doing EQ in the digital domain is superior to doing it in the analog domain.  Every analog equalizer I have ever heard does serious damage to SQ, in my opinion.  Also, if your ultimate goal is to use the two pairs of speakers you mentioned in your OP, then I recommend you set them up in your room and listen extensively, BEFORE you evaluate the need for EQ.  (Again, if paralleling two 4-ohm speakers is not recommended with your amplifier, then explore connecting them in series for a net 8-ohm load.) With two pairs of speakers, you will have a lot of flexibility to cure perceived room problems by re-positioning the speakers.

"...Any suggestions?..."
"... I’ve always been an early RS Infinity guy..."

I use to stop by a little shop, Woodland Stereo, where Arnie Nudell and Walt Lewsadder worked on the original Servo Static loudspeaker. Walt and Arnie would do their best at blowing up every amplifier on the market and often succeeded.
Anyway, Infinitys love power, I’d try a Parasound A21. It’s got some guts and can drive that load.

P.S. I still run my RS1B woofer towers and my nephew has my RS2.5s

I’d love to hear a servo static I again. It was pretty spectacular back in 1971 and amazingly expensive at $2000. Can you imagine?

Any amplifier will work and sound better into a net 8 ohm load (4 ohm  speakers in series) than it will work into a net of 2 ohm load, assuming you parallel two 4 ohm speakers. Albeit some amplifiers can handle the 2 ohm load.

Infinity was man things, but having great impedance specs was not what they focused on, I'd be very careful.