Something is missing

Don’t go the fuse route. That isn’t your problem. That would be the last thing to upgrade when you have money to burn/throw away.

You can get better sound by connecting a good external DAC to the Z1.  Also, I had the same Rotel that you have and wasn't impressed with the sound and sold it.  That may not be your problem though as many people are very happy with it.

If there was an easy answer this wouldn’t be a hobby. It’s also why there’s such a thing as audio nervosa. Nobody said it was going to be easy. 😩

Are you experiencing the same sound with both sources? I would look at two things your phono amp, the one in your Rotel may not be that good, and as suggested above an external Dac for your Sony.  Possibly even look at replacing the Rotel.

I will second Jim Smiths excelent book. Its all about how to dial in your system to get the best out of what you already have. You might try moving your speakers closer together say about 8 feet and the same for your seating distance. That can improve dynamics and help minimize the effects of the room as well as keeping them away from the walls if posible.

I would agree on speaker position and seating position.
A lot of people make the mistake of thinking because it’s a large room they can space things out accordingly.
Not usually true.
Most people end up with speakers too far apart as everyone gets scared if they are just 6 or 7 feet apart.
IMHO just try reducing the speaker distance from each other and your distance from them and it just may surprise you.
I know Focal go overboard on recommending large distance between speakers but what's it going to hurt to try?
Cost?
Big fat zero.