I went from Neumann KH 120 A to Genelec 8050 to PMC Result6. I never compared the KH 120 with the Result6 directly, but we can go from left to right.
While the KH 120 is a great and very neutral speaker, I preferred the Genelec. In my room, it had a bit more resolution, better spacial imaging, better and deeper low end (no surprise as it's 5.25" vs 8") and the filters were more useful to adapt the speaker to my room. Overall I would still say both speakers are roughly in the same ballpark and some people might prefer the KH 120 in their room.
The PMC Result6 are very different from the Genelec 8050. They have much more resolution and even better spacial imaging. They are tuned quite bright and have rather lean bass. I would compare their bass frequency response roughly to a Genelec 8040 (not 8050) with bass roll-off set to -4 or -6 db - which is a good starting point for a lot of small rooms. The transmission line bass is different from ported speakers. Both Neumann KH 120 A and Genelec 8050 are ported and go from tight to a very loose bass within a few Hz - the change is very noticeable. The PMC Result6 change more gradually. You will have to decide for yourself what you like better, there's no clear winner in my opinion. Their dispersion is much wider, which allows you to get really close to them. I'm currently sitting 1.2 m away from them and I can still move around without the tonality of the speakers changing too much, which was not possible with the Genelec or the Neumann. I was and still am astonished of what these little speakers can do. The Genelec 8050 is almost muddy in comparison and has moved to my mom's living room since (she loves them).
Beware, the PMC will show you every weakness of your room and cannot be adjusted to the room (they only have a volume knob). If your RT 60 isn't flat, you will hear it. If they stand 5 cm too far apart, you will hear it. Prepare for a long period of finding the perfect position and improving your room's acoustics (which will most likely be expensive).
In my opinion, Genelec and Neumann both look for a very even dispersion and ruler flat frequency response, and therefore produce speakers that sound very neutral, look good on graphs, and work good in bad rooms. PMC sacrifices all of it to make a speaker that is exceptionally revealing and forces you to fix your room to have a great listening/working experience. I think they don't care at all how their speakers measure as long as they sound good. I mean their studio lineup, I don't know and care about their HIFI series.
In my opinion, it's not worth to switch from the KH 120 to Result6 for better bass. If you like the Neumann sound, I would get a Neumann subwoofer or the mentioned KH 150/310. The Result6 sound very different overall and might or might not be an upgrade for you. PMC does not have a matching subwoofer for the Result6.