Originally Posted by JumboJack
where to flick the active/passive on an amp.
The convention of input labeling on amps arose from a huge misconception regarding bass outputs. You do not need to use the active input on an amp unless your bass is so loud that it distorts the input. Typically, the two inputs are identical, with the active input simply padded. It is not preferable to use the active input unless you need to.
In any case, don't get caught up in the semantics of classifying active versus passive. What matters is the nature of the signal impedance. If there is a buffer in the circuit path, from an active pickup, or an onboard preamp, or perhaps something else, the output impedance is lowered. This is generally considered a good thing, for a variety of reasons. However, as you pointed out, it can cause issues when playing into equipment that is designed to see a higher impedance signal, or interact with the pickup coils' inductance. If this is the case, you will want to avoid the use of active components, by either sticking to a fully passive circuit, or bypassing active components. If you have active pickups, there is no way to have a high output impedance, unless you add something like an impedance matching transformer. If you have a preamp of some sort, with passive pickups, it may be bypassed, to allow for the high impedance signal of the passive pickups. When there is a mix of active pickups and a preamp, it is the same as just having active pickups; the impedance will always be low.
Note, however, that though the impedance of passive pickups is generally always high, there are some pickups out there with a low impedance output. This is more-or-less the same as an active pickup, except that there is an inductive reactance from the coil(s). Sometimes low impedance passive pickups are wired up to impedance matching transformers, to increase output and output impedance. In this case, you can treat them like regular passive pickups.