Sure, be glad to. I first replaced the Sovtek 8550's with NOS SED 8550 "winged C" tubes. There's two of those-the SED's are harder to come by these days but there's a couple of sources left (I got mine from the tube store). Apparently as they discontinued production some of the remaining, lesser performing tubes were put on the market, so be careful, but the SED Winged C tubes are what ARC used to use before they started using the Sovtek tubes.
The EH tubes are the 6H30Pi gold tubes-also got those from tube store. You'd need 10 of those for the Ref 10. Both the EH and Sovtek 6H30s are built in the same factory, but i was told that the EH's are the "Lexus" version of the tubes vs. "Toyota"/Sovtek, and read somewhere in one of the audio forums about another Ref 10 owner that was very pleased with the upgrade. In terms of 6H30's those are really the only two choices-there are some arguably better NOS (as in 30 years old) tubes (e.g., 6H30P-DR Reflektor's), but you'd be spending several thousand dollars and to be honest IDK if you could locate 10 of those anymore from a single location. The EH tubes are a noticeable upgrade from the stock Sovtek's and very reasonable-something like $35 apiece. I had put on about 100 hours on the original tubes burning in the Ref 10 and noticed an immediate improvement in the EH tubes right out of the box in terms of the typical sonic qualities you'd associate with ARC products particularly more midrange warmth and quickness in the sound.