Stereo pre-amps with dual outs for bi-amping and a subwoofer line out


Do they exist? Maybe I’m looking in the wrong places, but I haven’t seen any. 

Definitely not looking for an integrated or AV Receiver.
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I have not seen a standard preamp that offers this capability, other than DEQX products; which aren’t “standard,” per se. Peruse thru their install/config manual, the numerous bi/tri amp setup configs are in there.  They also support dual sub outs.  I own one and I don’t know if I’ll ever steer away from it.
You can run each ic to the sub's line input, then each ic from the sub's line output back to your monblock  amps.Not all subs have a line output but they aren't hard to find.This is how mine is set up.
The Anthem STR offers a LOT of flexibility/features, including your requirements: https://www.anthemav.com/downloads/str-preamplifier-manual-online-en.pdf
And if you don’t prefer a Parasound preamp, look at their Halo poweramps that have a preamp (passthrough) output. 
My McIntosh C2500 preamp has 3 separate pairs of outputs both single ended and balanced.
A point to be aware of is that most preamp and line stage designs which provide two pairs of RCA outputs drive both of them from the same output stage, and simply jumper the two connectors for each channel together inside the rear panel. And likewise for designs which provide two pairs of XLR outputs. From an electrical standpoint that is essentially the same as using a good quality splitter on a single output.

Also, in many (but not all) designs providing both RCA and XLR outputs the signal provided to the RCA connector is the same signal that is provided to one of the two signal pins on the XLR connector.

All of that applies, for example, to most Audio Research line stages and preamps.

And what that means is that the output stage of the preamp will see a load impedance equal to the parallel combination of the input impedances of the two power amps, which will be considerably less than the input impedance of either, and may be too low to be optimal for some preamps. For example, Audio Research recommends a **minimum** load impedance for most of their line stages and preamps of 20K. If say one amp has an input impedance of 30K and the other has an input impedance of 50K, their combined input impedance would be (30 x 50)/(30 + 50) = 18.75K, too low to be optimal.

FWIW, I have used the Audioquest splitters Yogiboy suggested in applications involving suitable impedances with fine results.

Finally, keep in mind that most powered subs have relatively low input impedances for their line level inputs, typically somewhere between 5K and 20K.

Regards,
-- Al
Thanks all for the comments and suggestions. I'm currently running a split signal with Audioquest, just looking for something a little more elegant and I suspected I wasn't looking in the right price point.

Not quite ready to put $3 to $5k down on DEQX, Anthem or Parasound pre, but I'll certainly keep my eyes peeled.

I find it interesting that in a world full of bi-amp + speakers, most stereo preamps leave the solution out of their equipment. But Al seems to have hit the answer on the head. And stereo preamps are dinosaurs nowadays despite being some of the most satisfying/frustration-free listening experiences. 

I see that zero tube preamps are represented here!

Also, I was honestly surprised to see Anthem on the list, I thought they went out of business, guess they just went out of the tube business. Good for them, glad they are still here. The business sure has had to change. Used to be 4 hifi shops in my town, all carrying different brands. Now I've got to travel 120 miles round trip to reach 4 dealers.
My tubed Schiit Freya has 2 single ended and one balanced out. The 2 single ended outs go to my main tube amp, and a generally not in use SS amp for "remote" speakers. No impedance issues noted, and turning the "remote" amp on has no audible effect on the main amp whatsoever. 
BAT pre amps have two balanced outputs 
Yes ...however, better sound can be had using only one pair of preamp out connections.   Listen carefully and  hear a smaller soundstage and less dynamic contrast.  Also using 1 amp of a higher quality  is better than bi-amping otherwise.
If you like tubes the PrimaLuna Dialogue Premium has extra pre -outs. I have a couple of subs hooked up this way but used to use an audioquest splitter on my last preamp with the same results. 
If the outputs are just jumpered at the preamp is there really any reason to bi amp. I can see it in a fully active system with external crossovers. I had a 3 amp Linn System like that and heard the difference. I can never really  say I have heard a difference with bi amping. Put the money into one better amp. 
Emotiva XSP-1 preamp has four outputs
All four can be set to full range or two can be set to high pass 50 to 250 hz and two can be set to low pass 50 to 250 hz
I agree with pkvintage. I currently triamp in an active stereo system and definitely hear the difference. I have removed the passive crossovers in my speakers.

In the past, with same speakers and tube amp I now use for midrange/tweeter, I tried biamping out of the preamp as you suggest, with a large ss amp for bass. Didn't like it at all.

BTW, in a setup as you describe all amps reproduce the full bandwidth, so not a good solution. In this case a bigger amp is generally better.
I think the McIntosh c47/c50/c52 preamps will meet those requirements.
Integra pre/pros permit bi-amping and they are reasonably priced and great quality overall. The new r1.1 can be had for 1600.00 refurbished and has 11 channels with all recent audio and visual formats supported (with exception of HDMI 2.1 - which isn’t useful yet anyway).  Older models permit biamping as well. 
I think the reasoning behind biamping is that the bass drivers can send artifacts backs to the amp which impact the quality of the higher frequencies thereby degrading soundstage and resolution. As to which is better, I agree that generally a better single amp would make more sense dollar for dollar.

That being said, I'd be interested in playing around with an active crossover :)
There are many technical reasons why active can be better. The key is implementation, as usual.
What you note is an alleged advantage of biamping and in my test it wasn't audible. Active crossovers, on the other hand, have proven sonically superior in my limited experience. And that was not with more expensive amps.

Do you use analog sources or just digital? I focused on digital and designed my system around that, so could take advantage of current technologies for actively crossing over.