Having read this entire thread, I think you should return the KH 310 pair. If the money didn’t matter then it would be very easy to recommend them as no compromise high quality monitors. But it sounds like they’ve blown your budget with little remaining for a subwoofer, room treatment, or more electronics if you need. And they also seem like overkill for your room which is pretty small and easy to activate.
I think by going with these speakers I simply encountered so many issues at the same time, and went into uncharted territory (high end monitors, room acoustics) and experienced panic-mode that froze my judgment skills.
I was pretty happy with my room, and even if I had a less than ideal setup (HS8 + AKG K240 MKII + an old computer) I was able to build my career with this gear, to the point where I prepared and conducted film music sessions in Abbey Road studios and many different orchestras in Europe. Plus mix and master my music that currently has millions of plays on Spotify.
So my setup worked. In Italy we have a variation of "if it is not broken, why fix it" which is
squadra che vince non si cambia ("Do not change a winning team.") And that's what I did here.
My favourite car is the Dodge Challenger. But even if I could afford it used, it would be a very silly purchase because it would create a quite significative set of problems: heavy taxation for Italy (superbollo tax, introduced in 2012 for newly registered cars exceeding 185 kW) maintenance and gas, to name a few.
Also, with these type of cars you have a 100% a guarantee you'll get stopped by police at each checkpoint. 100%.
So, if I wanted to feast my eyes, I would fly to LA again, see or get to drive those cars, and be satisfied.
Same applies here, I think. There was too much waiting for me down the road and I got overwhelmed.
I'm still paralyzed, with a KRK 10 sub on its way (the 12 was simply too heavy to carry in my studio, and I thought it would overwelm my room).
If you want to A/B your new and old speakers just set them up as a Mono setup - plug the old into the left and new into the right output -then switch from your DAW.. Sit them next to each other. Dont' just test with music - use voices too , news readers etc.. You should be able to hear the differences quite easily then. Single speaker - mono - is a very good way to compare a speaker.
It's what I did today, and what I was doing for two weeks before the Left speaker arrived as well.
It's hard to tell, honestly. This is so subjective that I'm not sure there's a point in writing down my thoughts, but I promised I would report back.
I also feel a little ashamed because I don't see a substantial difference that puts the KH310 in a different league.
Volume being equal, the KH310 feels warmer, and that's the most significant difference.
The music that comes out of the speaker also feels it's coming from behind the speaker, not from the front. It's not aggressively presented in front of you, and despite not using the speakers at midrange, it feels like it's sitting further away than it actually is.
No idea why, but the presentation of the midrange from the HS8 is more at the front, very forward.
The Yamaha HS8 also feels slightly cheaper in terms of audio quality, there's no doubt about it, but it's not the drastic difference you might encounter for example with a $50 Walmart speaker and a pair of HS5.
The ideal test would be using them in a treated room with a monitor controller and ideal placement, but we know this is not possible at the moment.
If something else comes to mind I'll write an EDIT at the bottom of this post, for clarity.
Sorry if it took me a while but I spent half of today with this volume knob crackle issue, and I'll email Thomann later because I want to send this Komplete Kontrol unit back ASAP.