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"Audio refinement has pre outs that can be used for this feature. But, not the main-ins. Do you really need that if you are using a powered sub?"
Only if you plan to use the crossover in the sub to "strip" the low frequencies off, send only the high passed signal back to the amp. This should allow the amp to not have to work as hard since it will not be reproducing the low frequencies.
Of couse you could just use any integrated that has a set of line level outputs. Run the integrated full range to the main speakers and use the sub to "fill in" the bottom end.
Arcam integrateds' have pre-out and pre-in. There is a switch under the cover between the pre amp section and the amp section that needs to be moved to disconnect them internally for what you want to do.
I tried biamping a Classe CA200 with the Alpha10 integrated pre-amp section and it was a bad match. Didn't sound good. Matches very well with Arcam power amps though. I don't know whether I overlooked something when I tried that set-up or not. Just wanted to mention it, so you could research whether or not the integrateds pre-amp section will match well with your sub.
NHew Bryston 100SST is a honey with 100 watts not 60 and can addd D to A bord and phno board but is pricey.You will find many at various price points with one output and some with two mif you ever want to biamp hoirzoantally.Rogue m,akes good all tube gear in new lower priced line and Mark O'brien can add output if you want I believe.Great integrated with upgrade path is the VTL 85 which has variable out for sub and then latter get a plsitter to ad matching power amp (exact same circuts) so you can get splitter to go to amp and one to sub.And since the integrated matches the power amp you could add second power amp horizontally and not only get 150% or power but have two or three way speaker because less demands are made of each amp.Has not mono conversion switch so you don't have to nail bite about going vertical or horizontal.Latter is less power but many times has much more finesse.More the better (haing two not one) for future.Go deeper and get hybrid.Not sure if beautifull Pathos Classic III (now) has out's but think perfect rig would be a used Unison.If you have one set of outputs that are variable you can often just get high qualioty splitter from godd company like WBT and you'll never hear difference having to spliy it.
But Unsion is new vae of prety lkeading edge tech where tubes do there best (changing \voltage and giving it's sound chracterostics there and output is mosfet where you won't get roll off at frequency extremes or weak bass.Also when you pockets are mopre ching-a-lingy you can get multiple level upgrades with wirring,caps,diodes etc.Read revview of upgrade Unison's at www.6moons.com or go to Underwoodwally whjich will send you to links for the upgrades.Come sin two flavors with SE puting out more power (130 versus 80 I think?).You'd like it.Check out Underwoodwally's site and look at Unison stock and upgrades for future.Many here hjave reccomended much cheaper optioon that I did but you hadn't mentioned budget.But you can find what you are looking for with above pplus my slightly higher priced reccomendations.
My communications with other audiophiles and my experience with integrateds says that putting a sub or any electronics in the signal between the pre out and main ins will have an affect (likely negative) on the sonics of your system. There are many integrateds that have seperate pre outs or in some cases line outs that can easily accomodate a subwoofer(s) without in any way affecting the signal fed from your amp section to the speakers. I recently tried the Dussun V8i intergrated, which is in my opinion one of the best bargains in audio and a very fine integrated. However it has pre outs and main ins too, but no seperate pre outs. So, with this integrated your only choice is to connect a subwoofer via the pre outs and main ins. Since I had subs I wanted to hook up, that became a deal-breaker for me and I returned the Dussun. For me, seperate pre outs are the way to go to connects subs.
"putting a sub or any electronics in the signal between the pre out and main ins will have an affect (likely negative) on the sonics of your system."
I hear this sort of comment all the time from audiophiles. It doesn't make any sense to me at all. Even the least expensive electronics are so clean, the only way you could detect it is to see it in the signal chain. The advantages of inserting an active bass management controller so far out weigh any possible signal distortion makes the additional electronics a non-issue.
Just my 2 cents.
Regarding the Dussun... Simply split the preamp out signal -- one branch connects to the amp in jacks and one branch connects to the sub. No separate preamp outs are required.