@klappertjedundas Are your images dimensional, in that they have proportional width and depth. If they are fully dimensional ss positioning shouldn't be much bother. Sounds to me like you're getting FLAT and FORWARD ss, that would be a bother. There was recent thread here that asked specifically about where vocals located in relation to speaker front baffle, I recall most members systems ss located just behind front baffles. This is not abnormal ss!
I hear two perspectives with good system setups. One is more forward ss, illusion of performers in room, second is more recessed ss, illusion of performers in studio or recording venue. You may be person who prefers second perspective. Or, your image dimensionality is lacking.
How did the imaging from the Unison sound comparatively to present setup did individual images have more depth. I'd find it hard to believe that push pull would have greater dimensional imaging than present setup. Your should have top flight imaging with your pre and 300b amp!
Have you attended to AC in your room, therefore, dedicated circuits, conditioning if needed, power cords? Bad AC greatly affects ss and imaging.
One can also manipulate ss with speaker positioning, further out into room would help deepen stage, more toe in could help. Room treatments, front wall behind speaker important, reflective surfaces would bring ss forward, diffusion and/or absorption would be worth playing with. I know of two treatments I can guarantee will manipulate your ss to greatest effect I've experienced, one is Synergistic HFT, the other Schumann Resonators. Put a SR on front wall, I guarantee it will suck that phantom center image rearward.
In the end, you may just be one of those people preferring more recessed ss, but this usually sign something about sound quality is bothersome. Forward ss can sound in your face if sound quality not exactly right. Once you get your system to sound like flesh and blood performers in room chances are you'll love being closer to performers. The fact you need them to be at distance from you is sign of something amiss. Your new amp and pre are higher resolving than prior setup, this is exposing some flaw elsewhere. Nothing wrong with your equipment here, both are top flight performers!