Klimt,
Very good discussion and great advice from your A'gon friends.
I'm going to point the discussion in another direction. I am in total agreement that a modern integrated will offer far superior performance than your Denon receiver. The unknown factor here is the strength of the emotional attachment between yourself and the Denon. My 40+ years of experience shows that this can be quite strong in many cases. The daily "feel good" sensation you get from a piece of gear that was a loyal companion through some of the most important cycles of your life is impossible to place a value on vs setting it aside for something that delivers an improved listening experience. Only you can make that determination. That being said it is possible to significantly improve the performance of the Denon the degree where it doesn't sound like it came from the same factory. Yes, "audiophile" characteristic are possible with significant improvements in warmth, detail, and overall musicality from the Denon. There are "mods" you can do at home if you're "handy" or the average hifi service tech can easily perform these. Plan on spending between $200-$300 for a 40%+ performance improvement. Will it match the performance of a modern integrated? No. But, it you want your old friend to look the same, operate the same, and sound like a product a couple of rungs up the ladder, then you can have it all. If this is interesting, I'll be happy to share some insights into our successes with "mainstream" audio gear. Not trying to drum up business here. We keep pretty busy and you can have this done locally. Just didn't want you to place the Denon in a Garage Sale or demote it to a secondary system if a performance improvement would keep it center stage.
An outboard phono stage (with decent interconnects) is recommended with this. If you like your DM630's there are some do-it-yourself mods you can perform as well. The goal here is not to fundamentally change the voicing the the B&Ws but to just get things out of the way that crush detail, dynamics, and imaging.
Best of luck in your pursuits.