Enjoy your forthcoming A/B-ing once all is in place.
I will say this about that...
the primary limiting factor using an HT receiver is always going to be the preamp/processor within it. Perhaps more so than the amplifiers it uses, provided a proper speaker set is selected to mate with it.
Even adding very good amps outboard of it might not be as satisfactory a result as you could want for, ultimately.
They'll help for sure, in control dynamics and dimensionality. tonally as well.... but at some point to gain better levels of performance, akin to premium sound quality, I'd suggest some thought on separating things into two systems.
there are work arounds like adding a nice pre with a 'HT pass thru' feature but at the least, another set of ICs along with the desired pre will then be required. If another space is available, I'd definitely recommend it. Some other options are there too, but separation is purely best.
Each amp selection I have on hand has been attached to my receiver at some point. SS, tube monos, and hybrid. None of those additions equal what they can sound like with a great preamp feeding them directly off some source.
How much better can/do they sound like that over the proc/pre in the HT Receiver?
A lot! Depending upon the combination, of course, a whole lot!!
Consequently keeping things in general on a similar and accordingly level playing field when adding amps will be a big help in more areas than one, but mainly savings and performance by not over indulging by stepping too far up the amp stair case.
Changing speakers then, might be a better thought
. Though I suspect yours are pretty good. Ive only heard the Cremonas, and some of the SF two ways.