Unless I'm forgetting something, the larger set of RCA jacks on the back you mention are generally a second set of (variable) outputs, maybe even using a nicer RCA jack than the ones you currently are connecting your amp to. If this is the case, you might want to try switching over to them to see if you pick up a little free performance boost?
Otherwise, to know if you have one of the inputs configured as a HT bypass (a volume defeated input that just passes full signal straight through the preamp to the outputs), if you don't have any of your original documentation, you'll probably have to give Klaus a call to see if he can look it up in his records by your preamp's serial number. As far as I know, all of the inputs are configured as variable (volume controlled by the Tempest) by default.
You could use one of the variable inputs as-is and just turn the volume all the way up on the Tempest (letting your HT receiver control the volume) in the meantime, but you would also then have to remember to turn the volume on the Tempest back down when you are done, otherwise when you change inputs to something other than your receiver you might accidentally get blasted with max volume signal (which depending on your speakers might go badly for them if it were to accidentally happen when the wrong song is playing from whatever source you select that isn't your receiver when it happens).
Short version: without documentation to know for sure, a call to Klaus with your serial number should get you sorted out.