Lots of good comments here - especially based on your current system. Advents are the speaker that started me on this road over 45 years ago. They were absolutely amazing. 45 years ago. I can still see that orange tweeter behind the grill on the melamine card.
I own Thiels (2 2's), they've been so amazing I've not wanted to or needed to upgrade since the mid-nineties until recently. And even then, only because I can't get them from the ex until this lockdown business is over! You definitely want to steer clear of Thiel with your
current amplification. Get it? Current?
Eh?
They're not as bad as Maggies, but still require an amp that can easily drive a load. I'm guessing you might have popped in over at the AG place, there's the Thiel owner's thread and a lot of love (as there should be). They can be had for a steal these days. But, I also can't think of anything above the CS1.5 that doesn't require juice and lots of room. And, probably some restoration work.
JBL's are an excellent recommendation, almost anything can drive them. TBH, it's almost impossible to go wrong with modern speakers, I doubt there's anything you could pick that wouldn't be an obvious improvement over the Advents. But I'm thinking you might want to consider upgrading across the board if possible.
I'd bet a nickel right now we'll be seeing some
serious discount sales taking place very soon as this lockdown continues. Some people will be liquidating stock just so they can keep the lights on. Also keep an eye on the used market - people who've not been working for a while, or have extra components will probably be trying to come up with a little extra cash.