I would expect your H390 to sound very similar to the Harbeths driven by the H590 - there is not that much difference between the 2 amps. I believe several of the Hegel amps in the Harbeth videos on YouTube are the lower powered amps. And... Hegel often uses lower powered amps to drive them in shows.
Also, you may note that the McIntosh MA252 is driving them in some of the most impressive of those videos, which is only 100 watts into 8 ohms and 160 watts into 4 ohms (Harbeth's impedence).
And... if you prefer a different sound after you've tried them for a while, they're very easy to sell. They will require a few hours of burn-in to sound their best (if new). But... for acoustic sounds... you'll have difficulty finding anything to match their rich, warm, airy, life-like sound and imaging... or... have to replace them with a pair of Quad ESL-57's!