Brian Ding---designer/owner of Rythmik Audio---recommends low level hookups over high level, but offers a couple of plate amps which include high level binding posts for those who want it.
I know the argument regarding feeding your main speakers and subs the same signal (from your power amp), but I consider that argument flawed. If the power amp were "perfect" (a straight wire with gain), there would be no difference between the output of your pre amp and your power amp (except in gain, watts, voltage, current, etc.). Assuming for the sake of argument that no power amp is perfect, the high level argument is therefore to add the same distortion (from the power amp) to the sub as your main speakers receive.
Let’s use a tube amp as our case study. Tube amps have long been considered slightly inferior to solid state when it comes to the reproduction of low frequencies (the Atma-Sphere OTL amps being one notable exception. A lot of the problems in tube amps when it comes to bass is the sound of output transformers, which OTL’s and most solid state amps are free of).
So with a high level hook up, you are adding the worst aspect of a tube amp to the one frequency band subs are made to reproduce: low frequencies. As the amp (presumably, and hopefully) does not suffer from that ailment in mid and high frequencies, your subs may very well be receiving a signal more different from what the speakers receive than if you were using low level connections.
At any rate, with a plate offering both high and low hookups, you are free to try both, and use the one you prefer. Rythmik Audio offers a few different amps that include both high and low level hookups. And all the Rythmik amps include a very valuable control: a continuously-variable 0-180 degree phase control, for time aligning your sub(s) and speakers. Most subs offer instead a simple 0/180 degree switch, which is of very limited value. A continuously-variable phase control allows you to find the best location in the room for the sub (in terms of bass nodes), and to then use the phase control to electronically "move" the sub (in the time domain. Rythmik labels the control Phase/Delay. Delay only, as it is obviously impossible to move the sub ahead in time.) so as to be in phase with your speakers.