Buy an Audio Research SP10 MkII or an SP11 MkII ?

Growlar: I like your idea of the evolution process. You will indeed enjoy the heck out of the SP-10. And then some day if you have the itch, persue that next level of refinements. But I guarantee you that so many newer products that you will audition will not make you dance and smile like the SP-10 causes you to do. Half the fun is discovering such a special product. So just go for it!
John

Growlar,
I've owned both the SP10 & SP11 with a D115. Overall, my preferance is the SP10 even though I ended up getting rid of it. As others have said, the line section of the SP10 is not up to par with the phono section. This is not really the line section per say but rather that to use the line stage, you have to switch off the by-pass which engages all of the front panel clap trap. The reason I got rid of mine in the end was I got tired of feeding it tubes. If I ever win the lottery, I will buy another of these and have it rebuilt by Great Northern Sound. It is a classic.

I owned an SP-10 and SP-11 too.I was not experienced enough at the time to really determine superiority of either unit.I did ultimately get an SP-15(I can hear the "HOOTS" from the tube crowd already).What I can say,with confidence,is that after sending this unit to Great Northern Sound,for a complete rebuild(their ref update),I have to laugh at some of the prices asked for todays top contenders.I now have a supremely quiet,and neutral linestage,coupled to an unbelieveably high quality phono section.Tube rolling(3 tubes in phono section)does not cost an arm and a leg,and does make a big difference.I now have a very high quality Avalon based system,and find the pre/phono to have NO signature,tube or solid state.That is the way I want it.I have a friend who had the exact upgrade done and is also ecstatic with the results.He is an experienced tube lover(as I have become),but both of us realise that a truly neutral sound that can be nudged one way or another(for vinyl)by only three tubes is a pleasure to listen to.Good luck.

I'm confused ... what does Tube Rolling mean ? I've got that Homer Simpson far away look on my face.

put the tubes on the floor and roll... which tube goes further wins : )

What sirspeedy means is swapping different brand and model of tubes (like tires on your car) and you'll get different performance. Some do better in (wet, ice, dry pavement, sand..) clarity, body, extension, and presence.
It takes a lot of lab test ( trial and error ) to get the best performace you want for your taste of music.
It took me over 50 different 6DJ8/6922/7308 (except CCa because they're too expensive) tube families to get the way I like on the SP-11 MK II. I'm not big fan of SP-10 because it sounded a little slow and thick for my taste.