NOS Tubes

Speak to Brent Jessee for NOS tubes, he's a great guy who stands by his tubes.....for new issue look into Rays Tubes, they are getting recognition for Chinese tubes

Call Brent Jesse recordings he can recommend the sound you are seeking at least $500-$1k depending on choices.

You should find out which tubes are used in the gain stage. Replacing those will have the biggest impact on character of sound as opposed to those in the driver stage mostly operating on unity gain. I am not familiar with Mcintosh MA352, but you should find out. If I have to guess, I would say 12ax7 are used in the gain stage and 12at7 in the driver stage.

I replaced JJ 12au7 tubes in my VTL TL 5.5 Series II amp recently with NOS Mullard CV 4003 and Wow! I still have JJ 12at7 tubes in the driver stage.  

You may consider changing driver stage tubes if you want to significantly alter amp's distortion character and output volume. But you have an integrated amp and this should not be an issue. 

Upscale just got a stash of nos Mullard  cv4024 / 12ax7.     They also have Mullard nos 12ax7.  

I picked up a 12at7 for my preamp.  Driver grades were $39.  Kevin's stash grade were $59 so I grabbed one of those.  

Recommendation is one way forward to discover Valve Brands worthwhile to be considered.

How does one ensure the purchased and received Valve is a Close to Factory Spec' measuring Valve ?

' Pig in a Poke Purchases ' are not easily avoidable when buying into Vintage Era Production Valves. I have even had Modern Era Production Valves, along with Vintage Production  be rejected following purchase because of the measurements that were taken after receiving them.