G'day mate,
It would seem that prices for replacement panels should be fairly affordable, especially the vintage line... but is clearly not the case!
Even over here, down unda things of this nature are quite pricey regardless of model.
My very first pair of ML ESL's were the SL3's. Partnered with a Krell integrated amp and Krell top loading CD player, with some Kimber Select cables, it was mighty fine- Woof!
Years passed by and I sold them off to a chap who was actually upgrading from his Sequel II's. Once all set up, I went to his place for a listen, and both were fabulous! He was using a full line up of Classe' gear, monoblocks and preamp, including a Wadia and Meridian digital gear, that I also owned. So, sound wise, yes the the Sq2 should sound great, and the SL3 driven with a top line pre-power combination will be a step further.
Sounds like something is definitely not right with your Sq2's... looks like the previous owner didn't divulge every detail about the speakers. Also, you didn't audition before buying... that's like buying a car online without a test drive! Oh well, might as well deal with what's required in order to get these stats up to spec. One thing for sure is, they're definitely not up to proper spec!
Also just to add: if after trying out everything possible within your means, after all, not everyone has similar finances... and things don't work out more positively then don't spend more than they're worth! These are vintage, and they were probably sold for a reason... now that you bought them it's your baby to deal with. So unless they have sentimental value, there's really no point in spending over 1000s of dollars to restore them.
OTOH, say it were a pair of CLS stats and you wanted to restore them to the CLSIIz's that would make more sense, simply because those are full range stats, not hybrids.
I would agree with others who've advised on upgrading...As pointed out, t's better to save up and go for either ML's just discontinued line, which was the Reserve Line (Theos, Ethos, Montis & Summit-X) or if finances permit, go for their new line up (ESL Classic 9 or the ESL-X). Both these systems are a long way from the Sequel series or any other series. In terms of resolution, transparency, inner detail, build quality, materials and workmanship, it's a very long engineering stretch in upgrades at every angle imaginable in electrostatic speaker design. The overall performance of these new stats are far superior.
The decision is yours!
All the best, RJ