@DJBonoBobo Thanks for the reply. I see you're a 310 user. Could you briefly describe them a bit more? I understand I won't get better bass, but do they ultimately have a better frequency response, a bigger impact? Are they smoother in the highs, more pleasant? Sorry for the questions, but I can't listen to them anywhere; availability in my country is very difficult.
I had two KH310 und two KH750 in my 15sqm room, along with 2 PSI AVAAs. After almost 10 years of trying to get them to sound perfect, i eventually gave up, sold the subs and AVAAs and switched the just two KH120IIs + MA1, of course. The 310s are in the living room now. If you look at the measurements, you can see the KH310 having a wider and less perfect directivity than 120II or 150. This means, if you have walls close to them, differences will be more noticable because of a bit more uneven reflections. They can play louder and deeper without subs, but i never needed that ability in my small room. Even my 120IIs almost go down to 30Hz with room gain, which is enough for me. Apart from that, all Neumann speakers sound very similar. Some say, mids of the 310 sound special because of the dome. In my experience, i don't know. Maybe in a very subtle way, but i don't miss them at all.
Under perfect conditions, the 310s can be very good and they work very well in my 36sqm living room, but my experience is, not in such a small room. As far as i know, they are made for regular studios which should be in the ballpark of 40sqm.
If you don't have it already, i highly recommend the MA1, but i don't think switching speakers or subs will get you any further.
BTW, the KH310II and also a new KH350 are expected to be released soon. I don't know a date, but there are already firmware files for these models in the MA1-software, so it is almost certain they will be announced not too far in the future.