Can excellent tubes transcend modest amps?

The price difference of most tube amplifiers has more to do with power supply, voltage regulation and output transformer quality than what type of tubes they use. Tube rolling is basically a tweak; so I doubt you're going to turn a $200 amp into a $1000 amp with just tubes. Also remember that amps made in China are much cheaper than elsewhere so the quality comparison shouldn't be readily assumed by a labor rate differential.

Answer: no

My first comment was that the better and more resolving the system, the more the qualities of NOS tubes would be appreciated. NO- They WON'T transform junk, and I fully agree that a well built power supply, quality caps, etc. ARE an absolute must for "high end" reproduction, but: Quality NOS tubes will still take a mediocre amp to higher level, and the differences will not be subtle. Incidently: A high-dollar set of Michelins WILL have more traction, and result in better stability, ride comfort and handling on ANY given car(providing said car didn't already have a better set of tires on it). Will they transform an Impala into a C6? Of course not! They WILL however make an improvement.

So a Cayin 70 0r 88 with a bit of tube upgrade may be the best of both world in the budget category?

A pair of these: (http://www.tubedepot.com/pa-6sl7gt-3.html), and NOS TungSol JAN CTL/6SN7GT roundplates or Sylvania JAN/CHS/6sn7W tall bottle tubes from the 40's as drivers in the A-88T would probably satisfy your craving for a taste of the high-end pie(entry level, but solid). That would depend on your SPL needs, and the rest of the source material/system/room combination of course. Personally- I'd use Winged 'C' 6550's(the latest iteration from the St Petersburg factory) as output valves, as I know them to be a very clean tube. Slightly more power with the KT-88's, and you could well be pleased by the stock outputs. You didn't mention your tastes in music, or listening levels. Be certain to buy matched/tested/certified pre-amp grade(very low noise) 6SL7's for the piece. Finding NOS 6SN7 "Grails" that are screened for noise will be tougher, but they shouldn't be in as high a gain stage anyway.