Upgrade Audio Research CD3 Mk11

Has anyone had an upgrade or modified their Audio Research Cd3 Mk11 with excellent results or connected an external dac that has greatly improved the sound quality.
I am based in the UK but would be willing to ship if the results were really worthwhile.
I have a tube preamp so wonder about the benefits of a tube dac.
A friend of mine has an ARC CD3 Mk2 and I own a CD7. The sound of both units improved when we connected an Exactpower EP15A. Similar results results were also obtained with a PS Audio P300 230V unit.
One thing you might try is a Shunyata Python Helix power cable. This made a substantial improvement on an already excellent CD player.
Microstrip, how did the sound improve in both units? Also, how is the sound different in the CD7 from the CD3 Mk2? This might help Flange with what improvement to strive for. I would be interested as well since I own the CD3 Mk2.
I had this player. It is excellent. I would not mess with it. Either get somethig else, like the CD7, or get an external DAC but you will need to spend a lot to get an upgrade from CD3MkII.
BTW, if you are not running it via XLR outputs, you are not getting the CD3 to perform its best. Run it in a balanced system.