here is a ?, if you have one s.v.c. 4ohm sub and bridge a 2 channel amp to it the amp really sees a 2 ohm load which isnt good for most amps now that i know, what if its a high current amp that runs in stereo or mono, say audiobahn's a2200hct, does that rule still apply?
High current amps are generally designed to power lower impedance loads and most good "regular" 2 channels do just fine at 2 ohm(4 ohm bridged). Assuming honest specs I've always just looked at the power ratings at 2 ohms to get an idea of how an amp will perform. If it develops twice the power than at 4 ohms then I feel confident running it at that level.
actually a 4 ohm load on a bridged 2-channel amp is the same load as a 2 ohm load if the amp isn't bridged (in stereo mode.) that's totally acceptable. in fact you jsut don't want to go *below* a 4 ohm load (speaker) on a bridged amplifier.
on a side note, as long as you stay within the rated specs of the amplifier in question, you're fine. most amps are made to be stable to 2 ohms (4 ohms bridged if they are multi0channel and support bridged mode.)
there are a few amplifiers that are stable to 1 ohm, 0.5 ohms, or even as low as 0.33 ohms, but as you noted these are high current amplifiers, and will be advertised as such in their specs.