I haven't purchased AMP7, I can only speak for AMP8.
AMP8 has much much bigger soundstage than Mojo, significantly wider but more important much much taller and deeper making for a more holographic listening experience. Not that Mojo is bad in that department, but just nowhere near the same level. AMP8 is as full bodied as the Mojo but there is much more air, separation is much better while remaining very lifelike and not artificial (which I don't like). You still get thick notes but with the air. I feel it's particularly important with the Phantom, it needs air from the source to really shine. Overall the presentation is much more layered, the sound is "richer". Black background I would say similar.
Bass on AMP8 have more detail, sub extends lower and it's better controlled, mid bass are leaner than Mojo everything feels more articulate there. Mids on Mojo are smoother but cleaner and more neutral on AMP8 but vocals are more forward and paradoxically smoother and more emotional with better texture and nuances. Highs, well, no brainer AMP8 has much better extension and just the right amount of sparkle. It's also faster across the frequency range. Last but not least while macro dynamics are not far apart, micro dynamics is better reproduced by AMP8 but that's also due to the treble advantage.
