^^^ @bdgregory is correct. The HT passthrough is a feature on a stereo preamp that allows you to use your stereo speakers and amp(s) as front mains in a 5.1 HT setup. If you do not plan to use your JE amps in the 5.1 setup, there would be no reason to do this.
However, driving one pair of speakers with two different amplifiers (one for audio, one for HT) can be a tricky setup. It can easily lead to speaker/amplifier damage if not carefully done.
To do this right, I would think that you would have to switch your speaker cables from your JE amps to the HT Receiver when switching to HT, and then back to the JE amps when listening to stereo.
However, driving one pair of speakers with two different amplifiers (one for audio, one for HT) can be a tricky setup. It can easily lead to speaker/amplifier damage if not carefully done.
To do this right, I would think that you would have to switch your speaker cables from your JE amps to the HT Receiver when switching to HT, and then back to the JE amps when listening to stereo.