I've been wondering what style of EQ some of the production model pres have. There is a schematic for the NTMB floating around. It uses inductors for the mids. I haven't found any others though. I would assume most use standard active style controls, like a graphic EQ. A few use variable filters, like the Alembic, ACG, and Wal. I would assume the Glock and Aguilar are similar to the EQs in their respective amps. Do any of them use older amp topologies for their EQ? I'd think some of the East pres might, but otherwise I doubt it. Any that use a Fender/Marshall tone stack, or a Baxandall? The EQ (even flat) contributes to the tone considerably. Using a vintage tonestack may add an interesting flavor. I've heard the stereotype that active basses sound more 'hi-fi' quite often. The buffering may have something to do with it, but I think that the EQ has an effect too. I don't think anyone would call a Fender preamp 'hi-fi'.