So I just bought a Hegel H390 and

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A square room (15x15) will be difficult to impossible to tame the bass nodes. The speaker choice should be your's and your's alone. Many will work well with your Hegel but try to find one that satisfies your listening tastes. You'll have to get out and do some comparative listening and don't forget that a speaker will never sound the same in your room as it does anywhere else. Good luck!

Pretty hard to go wrong with something from Sonus Faber,Dynaudio or Dali..  Not a big fan of Dali but the Sonus and the newly designed Dynaudio are very nice.

The Hegel I would not say is a warm sounding amp.  In fact in comparing it to the old BEL Audio amp recently, the Bel being a very good class A amp was more musical and warmer sounding.

Depending on your musical tastes, look at a used pair of Vandersteen 5As, Verity Audio, and Ascendo speakers as I have seen very good used prices on there speakers.  The newer Ascendo speakers are excellent if you can find them.

Happy Listening.

I'm extremely happy with the Dali Opticon 8s I just received. Not familiar with Hegel as I am using a Parasound integrated.

Spendor Classic 1/2, KEF Reference 1, Sonus Faber Olympica Nova II, Sonus Faber Electa Amator III, Harbeth 30.2 XD, Spendor D7.2 are all speakers at around the 10k price point that I've heard and liked. I'd probably go for the KEF if I had my pick, with the Electa Amator not far behind.

Harbeth Speaker