This will fit the bill. Great price also.
There is such a beast, the Parasound Classic 2100 stereo preamp. It even has a built-in MM/MC phono preamp. But it lists at $599. I've sometimes seen factory refreshed ones at Audio Advisor for $399, but they don't seem to have any just now.
Here's another alternative: a used Outlaw 950 7.1 channel pre/pro. That's what I'm using for a line stage right now, and I used it until a couple months ago as a pre/pro feeding a 2.1 ch. system. Although it's physically bigger than a 2-channel (or 2.1 ch) pre would typically be, you can configure it for 2.1 channel, and in addition to all its digital 7.1 channel modes, it also has a stereo bypass mode and an analog bass management circuit. So you can use it completely in the analog mode, and make use of its internal bass management to send signals above 80 Hz to your satellites and everything below to the sub.
Two more things: 1) The analog line stage in this unit (you have to turn on "stereo bypass" to make it kick in) is a good, transparent, musically engaging line stage. 2) There is a used Outlaw 950 currently listed for sale on A-gon for $300.
Outlaw RR2150, a stereo receiver has bass management features.
Also pre-outs. Too bad it is only about 700$.
Emotiva, of quality unknown, makes a fairly inexpensive preamp which also has bass management built in.
I don't know if either are 'stereo' output...
don't forget that bass below 80hz is summed/mono, anyway.
I use the preouts on my PSAudio GCC250 (integrated) to drive a sub and use its crossover while running the mains full range.