Budget Tube Amp (newbie)

Upscale Audio has some nice used tube integrateds.
https://www.upscaleaudio.com/collections/amplifiers-specials
Ditto The Music Room
https://tmraudio.com/components/integrated-amplifiers/
Also US Audio Mart - Tube Integrateds
https://www.usaudiomart.com/search.php?keywords=&cat_id=55&price_min=&price_max=&typ...

I have a PrimaLuna PL5 power amp which drives my 84db/W Spicas to almost as loud as I ever want
I also have a pair of tubes4hifi M-125. Their amp kits are great value and lovely sounding amps, but I wish I'd built them myself.

HOWEVER, we I you, I would first investigate upgrading the crossover caps in the Advents.

+1 on PrimaLuna PL5  find em used for 800-1000..Autobias too.

Why are there so many Cronus Magnums for sale? Many are the latest version and nearly new.

I'll recommend a used decware amplifier. 

Another option would be a hybrid integrated , solid state power with tube preamp section