I don’t think my comments will particularly help the OP (unless the ATCs can be taken back) but I’ll throw in my tuppence worth
First as a general point I agree with
@Woodface . My experience too is that speakers make the biggest difference to the overall sound. Irrespective of whether you call it ‘sound quality’ they have more impact on the character of the sound than any other component. I do subscribe to ‘rubbish in rubbish out’ but the change in
character has never been as great for me with a change of CD, amplifier etc as changing the speakers. They have such different characters they can amaze or disappoint easily with the very same electronics. I’ve demoed many many pairs of speakers with the same electronics and been very surprised how different they sound. Hence when people come on here raving about PMC speakers for example I roll my eyes as I find them dry and uninteresting. But that’s me - some don’t find them that way
What exacerbates this is having the same speakers for years. Your ears/brain really do get attuned to ‘that’ sound and it is quite hard to adjust to a different sound.
So I wouldn’t change the electronics if you don’t like the speaker character. The overall change won’t change that much. You might get more detail, soundstage etc but it won’t change the ATC character by much.
This bit won’t help but I’ve always been disappointed with larger size ATCs (50s). I’ve owned and loved small ATC standmounts, even the passive 40s (MkI) and their integrated amps. I was just very disappointed with passive 50s. Did nothing for me
I’ve no idea whether the OP can change the speakers without losing out but the range of actives is more limited - otherwise you have to factor in an amp. Don’t throw more money at electronics if you don’t like the signature sound of the ATCs!