upgrade ARC SP-8

I am running ARC Classic 60's amp, new caps tubes and resister upgrade; with ARC SP-8II pre; Martin Logan CLS-1's; and ML Depth sub. I am looking to upgrade the pre. I am worried about mixing newer tech with an older system, If I spend the bucks will I do not get the bang. Any suggestions on what to look at?
FWIW: looks as tho' you like the ARC sound. My friend here owns an upgraded & modified SP-6A. Gorgeous sound & I can understand why ARC had its haydays during the times it manuf. the SP-6 --> SP-11. The SP-6A is a 1978 vintage pre but I think that, after modification & upgrading, it'll hold its own vs. many of today's $2000-$3000 preamps. Of course, MHO.
So, I recommend that you call up Steve Huntley @ Great Northern Sound & speak to him about modifying & upgrading your SP-8 Mk2 i.e. hang-on to your SP-8 Mk2!
Mods that should make your pre much better are basically to the power supply & to the coupling caps.
Modifying the RCA jacks (believe it or not) also makes a diff.
Punching a hole in the chassis & installing an IEC so that you can use an after-market powercord will also help.
Use of NOS tubes in key locations (the 1st tube in the phono section of my friend's SP-6A is a NOS. I forget which one tho) will also help.
There is much more life left in that SP-8 Mk2 than you'd believe. I say this after experiencing my friend's SP-6A & would never have believed it until I heard it. BTW, he still owns that pre & is not considering giving it up.
I gotta second that recommendation. Steve did wonders with my SP9. I think you'll find that Steve will give you very objective insight on what your preamp is capable of and how that may play into what you want from your system. It would definitely be a well-invested phone call. You can find contact info at http://www.greatnorthernsound.com

Good luck!
I would sell the SP-8 and get a used SP-16
and buy the phono stage for an extra $400.00 .
Don't get me wrong the SP-8 is great I use to own one,
but its getting up their in age and to many things may go wrong with it.
Great Northern Sound,also,did WONDERS for my Audio Research gear.A friend's as well!!
If you have become accoustomed to the SP8 over a long period of time you may be surprised by what is now available, and you may not like it! With the emphasis over the past 15 years or so on reproduction of detail a lot of the stuff available is on the bright side of neutrality, especially when compared to your SP8. Shop carefully and don't sell your SP8 'til you've listened to its replacement for a while. I'm still trucking along with my old SP10, faults and all. If I wasn't into vinyl I might change my mind......FWIW.
If you have a SP-8 MKII you might want to hang on to it; it is an excellent preamp; I don't know what you would get for the same $ that would be more pleasing. As for mods, I'd be very careful; you won't know what you have until the parts are changed out - just adding new technology with good specs isn't an assurance of anything except likely different sound. What you have is an all-time classic and I think you ought to leave it as is; Newbee's advice is right on the mark; keep the 8 II and buy whatever you think might be better; once you are sure the new preamp is truly better you can easily sell the ARC - but I'm betting it will be hard to find something considerably better until you spend considerably more. I've heard the SP-3A1, SP-6B, SP-8 MkI (original), SP-8 MkII, SP-10 MkII, and the Ref 2 MkI. You can make a strong case for why the SP-8MkII is the most "livable" of them all (great sound, reasonable price, easy to maintain).
Newbee,don't make any excuses for your decision to hang onto your SP-10.I had one,and it is a great unit!!!If you want to explore possible further improvement,you can speak to Steve,at Great Northern Sound.Otherwise,what you have is DAMN GOOD!!I should know,I had one,before I moved to another State.
Jam840, you will have a tough time improving on the SP8II. You will certainly have to spend big bucks. The SP8 is a really good preamp which is very tough to beat at any price. The SP6 is also good but not in the league of the 8. The 8 has a great midrange and is just musical and involving.