It really needs a proper input module. Not only will something like a Doepfer A-119 bring external levels up to the right voltage, it ALSO provides an envelope follower, which is a circuit that translates amplitude (incoming audio) levels to voltage levels, plus it also provides a gate output so that, as long as your audio is above the gate threshold level, you'll have a 5V gate signal to do things like fire/sustain envelope generators for use on VCFs, VCAs, etc.
A typical sort of A-119 patch would see outputs for your audio (now amplified to the correct synth level), the envelope follower's CV out sent to a VCF cutoff, and the gate out to an envelope generator or, if you just want on/off action, directly to a VCA in the audio path. By doing this, you can change timbre via your input signal's dynamics while also firing off a gate pulse for some other purpose. Useful.
As for the Behringer 914...filter banks are more like equalizers, not filters...despite the name. You can force them into resonance, though, if you use an attenuator to put together and control (CAREFULLY!) a feedback path from the 914's output back to its input; more than likely, this is what you saw being done. But this isn't going to yield the sort of results (and possibilities!) of a proper VCF, especially since there's absolutely no "VC" going on with a filter bank. Hmmmmm.......
EDIT: Hawt damm...OK, I whipped up something in an Intellijel 7U x 104 hp cab that's rather different. For one thing, it's got SIX inputs! Have a look:
So, there's two channels of input in the tile row (with level controls) and those are for feeding the two Ladik envelope followers below. Then you've got four more direct line-to-modular level converters over in that area as well for feeding audio without attenuation controls. But let's look at this a bit more systematically...
Tiles: Two channel input (fed by a pair of 1/4" jacks in the cab), single channel MIDI interface (also via a connector on the cab), Noise Tools (sample and hold, clock, slew limiter), DuATT (two-channel mixer/attenuverter/offset), Dual VCA, then a mono effect send/return and 1/4" dedicated jacks for that, and lastly, your level-controlled stereo out. As for that mono FX part, since you've got an outboard spring unit, I opted to keep that out of the modular and use these to let you put the spring into the system. This keeps crashes from random bonks and thunks on the modular from causing BLAAAAANG.
Top 3U: Quad level shifter, two envelope followers, then Noise Reap's Paradox dual(ish) VCO, with a Veils, a dual ADSR from Doepfer, then one of G-Storm's SH-101 VCF clones and an SSF ADSRVCA; those last five modules are intended to give you a hefty bass voice on the bottom end, using one of the best sub-wrecker VCFs around. And then...it gets weird! Next up is a Limaflo Motomouth...a vocal formant VCF, which lets you impose voice-like wahs on an audio signal. Alright's Chronoblob2 is after this, it's a killer delay line, capable of stereo or mono operation...and in mono, you get that twisty feedback path insert to play with. G-Storm's nice, gritty chorus cloned from Roland's JP-4 is after that for some dirty swishiness. Then we get one of Xaoc's devices, their Kamienec 4/6 stage VC-able phaser. Then next is Synthesis Technologies' Deflector Shield, which gives you a real frequency shifter for trippy detunings, wild, out-of-control phase effects, bending sounds into metallic FMed clangers, and so on. And the little white sliver at the end is a Konstant Labs PWRchekr to keep an eye on your DC rail conditions.
Bottom 3U: More Noise Reap trouble with their uLoaf, which is an LFO (per)version with a lot in common with the Paradox VCO in terms of interaction between the two circuits. Not so much a repetitive cycle thing, but more wobbly and weird. Maths (of course) next, then the Tiptop MISO lets you cook up more modulation signals from the sources by generally messing with the behavior of the modulation module outputs. The other source is the Intellijel Quadrax/Qx combo, offering two or three stage envelopes, CVable LFOs, etc etc. And the MANUAL modulation control, a Doepfer A-174-4 three-axis joystick with onboard "joystick math" outputs, allows you to add your own hands-on touch to many different functions in the build. Mixing gets done by the TexMix setup, with four mono inputs and four stereo, and given the high flexibility of the TexMix system, it lets you break out things via the outputs, the two AUX sends...PLUS you get four more VCAs over your audio on the mono module. And with the DOUTS module, you can even take a direct output from a single strip on the TexMix and send that separately to the DAW.
The idea here was NOT to create a typical modular synthesizer. Instead, I took a few cues from explanations of how Tubby's Dromilly Rd. studio plus Lee Perry's original Black Ark were set up, and cooked up a box here that can be dropped in to deal with a lot of that functionality, while making additions to the module complement that can work for the old-skool dubplate sound as well as the newer Deutsche Dub sounds. Now, to REALLY open this thing up, I'd also suggest some of the following...
First of all, you need some crossovers. Get as many bands as you can, because you'll be using a pair of these to split up parts of incoming mixes into different frequency domains. I use a pair of four-band mono crossovers from Wheatstone/AudioArts for this, then what I use NEXT are several of THESE: ZRMAAOSwEmlZ1RpV" target="_blank">https://www.ebay.com/itm/132351591652?hash=item1ed0c504e4ZRMAAOSwEmlZ1RpV Not necessarily that exact model, but Krohn-hite is THE name to know in outboard filters. Anyway, what I use these for is, once the crossovers have done their job of bandsplitting, these various Krohn-hite (and here in my studio, a few others) filters let me "zoom in" on a specific sound. This sort of thing is especially effective with the envelope followers, as you can use a VERY tight bandwidth on one specific sound to trigger one of them. You could even be putting some OTHER sound under the control of the envelope follower to create a "ghost" based on the original extracted sound's envelope...but NONE of its spectral material!
In short, it's a box of dub trickery and general sonic weirdness that goes along with that. Put to the proper use, I doubt you'd ever really hit the limits of what it can do, particularly if you've put it into your studio's workflow in the right place (right by the mixer, tbh!).