First off, just want to say, it’s late here where I live, so haven’t read the other comments in this thread.
Secondly, if you found a Meridian 504 for $140 consider yourself blessed and lucky.
Third, I’ve owned many many tuners over the years and the 504 was the only digital tuner that I truly loved. Don’t bother with anything else, just keep it and enjoy it. It’s a truly great tuner!
Lastly, for a good 5-6 years, I was running 2 tuners and switching back and forth between them and the differences were negligible. The NAD4300 is a superb tuner as was the Perreaux TU1 and super rare PS Audio ST1. Those were some of the latest tuners that I’ve owned. A modified Dyna FM3 is also a wonderful tuner as is a Pioneer TX9800.
With so much cool used gear out there it’s sometimes very hard not to want to try everything you can but the grass isn’t always greener on the other side and you need to be happy with your lot. Being happy with your lot in life (whatever that may be) is the key to happiness in life.
Enjoy the Meridian! There’s not a lot out there that’s so much better.

