It just so happens that I have exactly these two amps. I got the Hegel H390 about 6 months ago. Using B&W 804 D3 speakers. It’s a very good amp, but felt the DAC could be better. I use Roon and was missing native Roon support on the Hegel. I brought a friends Topping D90 (MQA) DAC, and connected to the XLR of the Hegel - and the difference was absolute.
Then I heard the new Krell K300i at a friends place using same speakers. There is something magic about Krell and B&W speakers .... and managed to convince myself that this was the time for me to do something I have been wanting for a long while. I got a pair of Magnepan LRS for my living room with the Hegel H390 - and have set up a new Krell K300i in my listening room for the last 4 weeks. No difference of using a Topping DAC with the Krell ..... the Krell is absolutely fantastic if you listen to rock, or classical. Huge sound stage, and very warm. The Hegel sounds extremely refined and drives the LRS beautifully - specially for vocals and instruments.
I don’t think I can say one amp is better than the other. I find the Krell has more dynamics, is warmer and just overall body (I haven’t been able to go about 42 on the volume dial of the Krell). Even though the rating for the Krell is 150 watts - it feels like it has a lot more power left for sure. The Hegel H390 is very refined, and does not have Krell’s dynamics - but better for certain kinds of music. The DAC in the Hegel could be better.
Hope this helps, and happy to share my experience - without picking one over another.
