There's the issue of burn in - and then there's the issue of tube warm-up. I don't think you experienced the full flower of the CD player's burn in after two hours (granted, I've never heard the unit so I can't know - but burn in ususally, not always, but usually takes a bit longer). Tube warm-up - a vital thing for tube listening is another deal altogether. Tubes will not produce sound at all for the first 30-60 seconds they're on. Then they fuzz into life and sound dead and lifeless for an indeterminate period. I generally find (with gear like my Dynaco 70, or ARC Classic 60 amps) that music becomes listenable after 2-3 minutes and gets audibly better for the next 30-60 minutes (pretty dramatically better over the first 20 minutes - then very subtle improvements in speed and transparancy after that to the terminal level after about an hour). Now, preamp tubes may take different periods, and I imagine any given tube will take a varying period to warm up over its life span, and at various starting operating temperatures etc... The point I'm trying to make here is that you probably didn't need to put on "endless repeat" (a burn-in strategy) for 2 hours just to hear your tubes warm up. A quick 5 minute trip to the mailbox would probably suffice to get you started most days...
