1 preamp out to a 2nd preamp in any harm?

I like the KISS principal myself but whatever floats your boat. The more things you put in the reproduction chain the farther it will be from the original sound but if that does not bother you go ahead.

I think what you want is very common and one solution is to use Y connectors on a single preamp's main outs with one leg of each going to 2 different amps. That would be less likely to distort your distortion in chaining preamps.

Luked. Yeah your idea is a good one. then you can control the volume of the sum a little better.
Have the sub preamp follow (or be connected from or after) the main channel one. then the main channel master control is all you usually need to move. But if you want to adjust the sub in relation to the main, then the sub pramp volume can be moved.
Connecting the second one via volume controlled output is best. If you use the line out, or tape out, everytime you change the volume on the main, your sub will need to be adjusted. (which is a PITA)

And yeah, maybe using two may cause a slight degredation of some theoretical signal. The thing is, if it does what you want, that is way better than somebody elses 'theory' hey!

I don't understand several things about this:

1)The woofers in the main speakers will presumably be handling much higher frequencies than a sub would normally handle. Assuming that the overall setup is intended to provide stereo (is it?), I don't see how it would make sense to provide a mono signal to those woofers. Driving a sub with a mono signal can be appropriate only because the frequencies it is reproducing are very low.

2)How are you generating the mono signal?

3)Assuming the sub is a powered sub (is it?), containing its own amplifier and providing a level adjustment, I think you are saying that the reason for including the second preamp is to allow level-matching between the woofers in the main speakers and the mid/hi drivers of the main speakers. Am I understanding that correctly?

4)Can you indicate the make and model number of the sub, which may help to clarify some other things I am uncertain about?

Regards,
-- Al

There are a couple of unique problems with the current set up. The Sub has a rythmic plate amp that produces a hum in the system when connected via RCA, the hum disappears when connected via speaker inputs. The mono signal will be generated via y output from the preamp going to the monoblock. The monoblock will connect via speaker wires to the crossover system in the rythmic plate amp with one feed going to the sub and one feed going to the woofers. If this produces distortion or an echo effect I may just run a mono feed to the back speakers from the sub. Again I have know idea what this will sound like I just do not want to destroy anything finding out.