garth,
first of all, what you want is the preamp connected only to the main 2-channel stereo speakers/amps. and, the surround speakers connected only to the ht receiver's surround speaker outs. (if you have subs that are used for music as well as ht, i would recommend having them connected to the preamp for music use, not connected to the ht receiver's sub outs.)
then, there are a few wariables that need to be known. does your ht receiver have preamp outputs? and will the receiver still drive its internal amps while simultaneously driving its preamp outs? if so, then you could run the tape out from the preamp into a line input in the receiver. then, from the receiver's preamp outs, connect to the preamp's tape input. then, the ht receiver's wolume pot would also control the wolume of the preamp. (you have to select the "source" of the ht receiver to whichever line input you have running from the preamp's tape out.) when you wanna engage the ht receiver, simply engage the tape loop on the preamp. your actual movie source, of course, needs to be connected to the preamp, not the ht receiver. and, you will still have to set the preamp's wolume pot as needed to match the surround speakers connected to the ht receiver. but, once set, the receiver's wolume pot should be able to control everything. i would suspect that, when using the ht wolume pot to control everything, the preamp's wolume pot will likely need to be max'd out, or near to it, as the signal it sees is being controlled by the ht receiver... exact setting will depend on how much gain your main stereo map has, and efficiency of the stereo speakers vs the gain of the receiver and efficiency of the surrounds.
but, even if your ht receiver can't do this, you can still run a line out from the preamp to a line in on the receiver; in this case, you will likely have to set the ht receiver's wolume pot to max, or close to it, as the signal it sees will be controlled by the preamp's pot. once initially set, there should be little need to be adjusting both pots... and again, final wolume pot setting will be determined by amp gain/speaker efficiency as per above...
all that said, even if your receiver can be configures per the 1st scenario, i think i'd go for the 2nd one, simply because i bet the preamp's wolume pot will be more transparent than the receiver's; i'd rather have the receiver's wolume pot max'd out, and have the preamp's pot controlling the mains and the surrounds, then having it the other way around...
and, a 3rd option is simply running a line from the preamp's tape outs to a line input on the receiver. in this case, the wolume pot of the preamp and the pot of the ht receiver will have to always be separately adjusted, as the receiver will always be seeing full gain from the preamp, even when the preamp is turned all the way down. but, it is certainly the easiest way to connect things, and once you are used to using it, separately adjusting both pots should not be an issue, cuz you will know how one pot needs to be adjusted in relation to the other at any given listening wolume...
iirc, you were considering this melos locally, and it is used? would the seller allow for an in-home audition? if not, you could always find any old preamp to try, yust to do a "dry run", based on the above... and, if you're wanting to try the 2nd option, and a preamp does not have two line outs, simply get something like these (awailable at parts express):
hth,
doug s.
