Jadis JF-1 Crossover? Any experience?

T-bone -- if I understand correctly: you have a pre, you have an active xover for yr particular speakers, and there is no passive xover doubling up in the system. You also have one integrated amp + 1 power amp. Correct?

1) You set the two amps to ~equal sensitivity using the volume pot on the integrated. Then you control system volume via the pre volume control. OR, if you have attenuation @ xover level, use that instead and play yr integrated at full or optimum level.

2)

Does the crossover internally take care of the difference in sensitivity that the speakers it was meant for

I wouldn't know. Can't Jadis advise on this? I see quite a few controls on the pic; what are these -- or, failing that, why don't you check the output @ the xover point, 1-2octaves above & below.

3) I'm a bit confused...sorry. You already have 1 volume control on the integrated to "match" (hopefully) yr two amps' sensitivity. If you're asking about a passive xover -- then the volume "control" becomes part of the xover circuit. Best to use an Lpad. Is this what you're asking??
Cheers

3) Penalise? Not really. Plus it's a grand pain to avoid gross energy losses and impedance disasters when using many attenuators. You have attenuation already designed into the circuits -- use those.

2 These xover pots are useful to "equalise" the sensitivity levels of yr two amps (i.e. so that they output the same power/voltage level for any given input).

You might want to set the integrated at unity as you note, and then compensate for low-level listening every now & then by upping its volume a bit...

Overall, the scheme should work very well.