They are both very nice pieces and sound great. With the right pair of speakers, the Nova 300 can dig out a lot of detail and music sounds natural. The best speakers I've matched it with are my Klipsch Heresy I and Focal 1008 BE. If your speakers are more on the "warm" or "neutral" side, it might sound a little "flat" or "boring". It sounds good with "detailed" speakers.
I use the DAC for streaming and it is actually very good, so if you do decide to send it digital files, it'll work great for that. Better than my Wyred 4 Sound external DAC. It has a decent headphone amplifier and a phono stage. I haven't tried the phono stage, so can't comment on that.
The power ratings seem over-inflated, at least in comparison to solid state and tube amps that I've owned. It will play loud and clean, but the "300 watts" of the Nova 300 do not compare favorably to the 180 watts of my tube monoblocks. It's more like the 50 watts of my ARC VSI55 integrated. The 440 watts of the Grand Integrated also seemed over-inflated. If you have power hungry speakers, the Nova 150 might not have the grunt to do them justice.
I have no experience with the Hegel units, so can't provide a comparison and I'm not sure how you classify "audiophile" vs "upper end mid-fi", so can't comment on that either.