I also love industrial music...here's my thoughts:

I own the AS-500E (EMS Synthi Clone) that you mentioned. it is
AWESOME!!! it's a diode filter.

Doepfer also do a Doide filter called A-102...and i think it's their
BEST filter...really unique and awesome sound - LOVE IT!
it can be warm and juicy or cold and harsh....it's got the wildest
RES on it! ...and it's one of thier cheapest filters.

A-120 is not my favourite...it's a little plain.

> For example, you can get a low pass filter, high pass filter
> or band pass filter. Is there a Doepfer module that maybe has
> all 3 combined where it's

A-124 WASP filter is a 3 in one...and it's also brilliant. very harsh
and distinctive sound.

> Also, I've heard mention of "sub-oscillators" somewhere.

the A-115 is kind-of a sub oscillator...it gives you several "sub
octives" to fatten the sound up. it's inexpensive and very useful.

we have a few YouTube thingies that use heaps of Doepfer stuff:
http://www.angelspit.net/blipvert/

Doepfer stuff is BRILLIANT for modulating and doing "tricky stuff"...!

ROCK!

ZooG.