Better Integrated Amp?

At your experience level the Denon would be a good place to start and having a new piece of gear with a warranty would let you focus on other parts of the system. Even the less expensive Denon 600E might be an excellent option since it has built-in Bluetooth that would let you easily sample new music using Spotify or another streaming service and its lower price would leave you more to spend on speakers which, in my opinion, would have more of a positive impact on the quality of reproduction.

You should check out Rega integrated amps. You should have no problem finding a dealer on your side of the pond!
https://www.rega.co.uk/products/amplifiers

I agree with sfar in that it would probably be a good idea to buy the Denon from a dealer who could possibly guide you towards some appropriate speakers and whatever else you need.  Just be realistic.  You say you prefer rock/metal that is often difficult to reproduce at even moderate volumes as opposed to string quartets and the like.  Maybe a nice pair of headphones? I bet the Denon has a half decent headphone jack. 

This UK based channel has some good advice. Here's one video but take a look at his others. https://www.youtube.com/watch?v=7EAJPpVvrpw&ab_channel=ABritishAudiophile

I can highly recommend the $599 (US) Rega Io integrated amp. The sound quality is amazing for the money. IMHO it sounds  much better than the Rega Brio that I compared it to. It only puts out 30 watts per channel so you will need to match it to appropriate speakers. I am using it with a pair of Tannoy Mercury M1's in my bedroom system but will be upgrading to the Vandersteen Wood VLR's when I can. My dealer shows it with Proac and Vandersteen speakers and the combination with the VLR's, even the $3K VLR CT's, is really good.

The unit also has a good phono stage and sounded great with the Rega P3 with an Ortofon 2M Bronze cartridge. You should check it out. Good Luck!