Newbee, I never made the effort to try other tubes in the SP-10 like you have. This perhaps would have helped a little with the 10's line stage performance, but the RAM tubes worked so well for me in the phono stage. I must have been a lucky customer of RAM tubes.
When I heard the LS5, it was so far ahead of the 10 that simply could not be entirely due to tube rolling. And in fact, when I got the LS5, I still had some RAM tubes which I used later on and they worked very well.
Yes, there were rave reviews on the 10 back in the early to mid 80s. But this was relative to its competition at that time. Keep in mind that all the reviewers at that time were using LPs as their primary source and for the most part, they could not stand the sound of CD playback.
Anyone who claims the 10's line stage (CD) capabilities to be excellent or even very good simply has not heard the incredible products from the last 10 years. But indeed, when used for phono, it has incredibly magical abilities like very few phono stages out there.
I can only imagine what an overhaul of this unit by Great Northern Sound could do to its capability. But the LS5 and PH2 outperformed the 10 in phono and by quite a large margin. By the time you got an 10 on the used market (typically running at around $2200 and who knows why!), and then paid for the upgrades, etc., for an overhauled 10, I feel you could be so better off to go down a number of other paths with newer products. If I sound very critical of the 10, it is only because I feel it was optimized for phono and because products like the LS5, PH2, BAT5i, BAT31SE, BATP10, AesthetixIo, etc., take music presentations to a whole new level that once you hear this, there's no going back to the 10. But for 8 years for me, for LP playback, the 10 had no competition....including the SP-11. For a full unit preamp, the CAT SL might just be the ticket.
And I have to smile and laugh at synthgirl's comment that the LS2 had no magic compared to the SP-10. I absolutely concur! When I sold the 10 I was sure the LS2 (along with the PH2) would be what I had wanted as a major "upgrade". The LS2 was hands down the most disappointing audition I ever had. I guess this was due to my great expectations. But hearing the LS5 minutes later at the same dealer brought back that awesome SP-10 magic but with refinements all over the place. The price scared the heck out of me but once I heard it, I knew I had found what I had been searching for. I just coudl not understand how ARC had products that sounded so very different: the LS2's analytical and sterile presentation and the LS5 with it's SP-10 like bloom and harmonic richness. The fact that Stereophile gave both these units a Class A rating was absolutely ridiculous!
So if you're only looking at CDs as a source, or other line-level sources, I would recommend that you sell the 10. From what these sell for, and if you want to stay with ARC products, you can get an LS5 MK III and you will never look back. Even the MK II in the $1500-1800 price range is a steal.
John