Audio Research VSi55 Tube Rolling

i am very happy with my new ARC VSi55 integrated amp, but have been thinking about trying a bit of tube rolling. the amp now has about 400 hours on it, and to this point i have only used the stock tubes.

i would very much appreciate specific suggestions that you might have. i am also interested to know if anyone has tried "cryoed" tubes in their VSi55.

FYI - speakers are coincident speaker tech partial eclipse II's, and CD player is musical fidelity A5.

Above should read unless that ARC amp was designed for KT-120, I would not just plug and play.
Hifigeek1, thanks for the input - I have seen mention of the quality decline elsewhere, so I'm on board with what you're saying.

Albertporter, I've already confirmed with ARC (and others have posted previously to the same effect) - the VSi55 takes the KT120 no problem. No word yet on the KT150, but the 120 is a go.

I'll probably go with the KT120 and see how they compare.
What's up in 2016?
Well I don't have good news for you guys...!
Recently, It was time to re-tube my good old VSI-55 so I called my local ARC dealer who said I could easily upgrade from the stock 6550  tubes to KT120 or even better the newer KT150...! To double-check I've called Audio Research directly and here is the BAD news the tech told me: While it will work to re-tube my amp with KT120 or KT150, the power transformer has not been designed for this, thus it will overheat tremendously and this will  seriously compromise its lifespan (a new power transformer of this type costs around $500-600 including labor). Instead he recommended to use the 6550's or KT88's... More interestingly, I asked if I could re-tube a VSI-60 (very similar amp to the VSI-55) with KT120 or KT150 and he said the same thing: NOT recommended! Then I asked him why they still offer the VSI-60 with KT120 on their website? He answered that thuis model was discontinued but there may still be some units are resellers. And the newer VSI-60 models had an upgraded power transformer to accomodate KT120's while older ones did not...

So be careful if you think this is a good upgrade... You may have better sound but you will inevitably toast your power transformer!!!

I called back the local dealer about this contradiction, he retracted and said ... listen to the ARC tech...:-)

Anybody had issues ...?