Connecting a sub to amp pre-amp outs?

Yes, you should be able to connect your sub to these pre-outs. Your manual says you can use these for bi-amping. If you think about it, since your sub most likely has a built-in amplifier, you are in essence, bi-amping to your sub's amplifier.

Normally this would be the preferred way to connect a subwoofer.

-IMO

Yes, it is done.
Go get yourself one or two quality "Y" adapter cables.
Place the "Y" adapter's from pre-out left & right (only use both if your sub has left & right inputs).
Run one set of IC's from the Y's to your sub and the other set of IC's (L&R) back into your pre-in (L&R).
This allows you to run your main speakers full range and hopefully your sub is equiped with pass filters to tailor crossover points.
This is probibly the eazest way to do it, there are much more involved setups you can use.
Hope this helps & good luck.

What subwoofer and for what use (HT or music)? Many subs (like REL for example) work much better for playing 2 channel music, if they are connected to the high pass speaker cable connection. The pre-out is usually better for HT surround.

The problem (I think --if I understand your set up correctly) is that if you output from the preamp outs on your amp to the sub you will not have control over the volume in proportion to the level you are playing the amp at.

Thanks for all the input. I am primarily a music listener. Thanks to all who have commented on my question. The sub is an Infinity Servo Sub which seems to match very well with my Paradigm Reference 20 v.2 monitors. My amp is an Arcam Alpha 8R integrated.

Reading Wizard454's comments, I'm not sure why I would run a pair of IC's to the sub from a Y adapter attached to the Pre-outs on the amp and then another pair of IC's from that Y adapter back to the Pre-in on the amp. I guess I don't understand the concept involved and it doesn't help that my amp's manual and the sub manual don't talk about that alternative.

If the sub has pre ins and outs you can go from the Adcom to the sub from the pre-outs of the Adcom then from the sub to your main amp. This means that you will be using the crossover in the sub and it may or may not be bad for the sound of your main speakers. I prefer to use "Y" cables if the preamp doesn't have two sets of pre-outs and send one signal to the sub and the other to my main amp. This way the sub can be set to roll off the bass at a low frequency such as 63hz and the main speakers can still run full range without the detrimental effects of the subs crossover.
Some prefer to use the sub crossover to take the bass out of the main speakers because it frees up the midrange and takes some of the strain off of your main amp. You can try it both ways and see which one you like.

Salby- Your Arcam integrated provides for a pair of pre-amp outputs to drive another amp (bi-amping). As Stehno is correct in that using these pre-amp outputs to your sub is the preferred configuration.

These outputs will function with your volume control. If I recall correctly, this is NOT an internal amp-bypass connection as found on some receivers which is what Wizard is referring to. As long as your sub has RCA inputs for both L & R channels, then just run a pair of RCA cables from the pre-amp outputs to the sub inputs. (The sub will sum both channels for you assuming it is a single subwoofer). Good luck.

Stehno is correct. I would hook up exactly as he describes.

Similar question. I have a couple preamps that have 2 sets of outputs. I usually run 2 channel and run one set of outputs to my sub and then run another set of interconnects from my sub output to my amp. Can I use the other unused preamp out to just go to my sub? So one output to my amp, the other outputs just to my sub in? 

If I've read these comments correctly would that just run the speakers at full range instead of using the subs crossover control? 

Using Vandersteen 2CE Signatures which are reletively modest on the low end.

Yes, yes and yes!

Yes, this should work fine, but take time to dial in the sub level again by ear, as you had done previously using the other connecting cables.

The notional benefit is that a lower-level (should be less distorted and less lossy) signal is passed to the subs, although this may be canceled out if the sub’s amps are themselves crappy.

You still need to low-pass the sub (use its crossover) unless there is some way to do this in your amp. I doubt it as otherwise this would be described as "sub-out" connections, not pre-outs. If you ran full-range, then the sub will be amplifying a full-range signal, causing overlap and distortion beyond the driver's useable range. Probably start around 100hz and keep going down.