Splitting a pre-amp channel for sub - good or bad?

Splitting the channel will work. I'm doing it because I use a tripath amp. You will see a slight lessining in gain.
I'm using a Lightspeed Attenuator and lost less than one hour of gain on the volume knob.
If you listen at 11 o'clock before the split. You might have to go to 12 o'clock after the split.
I didn't notice any degradation in dynamics or attack, just in gain.
I know every system is different, so it might be different in your system.
Good luck and let us know how it works out for you.

Not a good idea in this particular case. As we discussed in one of your other recent threads, you may already be approaching the point of impedance incompatibility between the preamp and amp. If you split the signal it is likely to make that situation considerably worse.

The input impedance of your sub does not appear to be specified, but line-level input impedances of powered subs are commonly in the 10K to 30K area, sometimes as low as 5K. The preamp will see a load impedance equal to the product (multiplication) of the input impedances of the sub and the amp, divided by their sum. For example, if the sub's input impedance is 20K it would combine with the 33K input impedance of the amp to produce an overall load impedance seen by the preamp of (20 x 33)/(20 + 33) = 12.4K, which is probably too low for the AES preamp, assuming that it uses an output coupling capacitor.

Member Bifwynne resolved a comparable problem very nicely, at modest cost, by using a buffer stage custom made for him by Tom Tutay. Search his posts for more info on that.

Also, driving the sub with just one channel is not a recipe for good sonics. The two channels should be summed together into a mono signal, either by the sub if it provides that capability, or if not then in the buffer stage.

Regards,
-- Al

Thanks guys, very helpful.

Al- very nice explanation, sounds like you've had a physics class or two before :)

Consider a sub crossover. Discontinued NHT X2's and Paradigm X-30's are getting hard to find. Bryston 10B Sub's are expensive. There's a European company called Reckhorn that makes something rather unusual, if it's available for US voltage.

Splitting is commonly done and typically does not degrade sound quality
Alan