I just tried the y connector. ... and the sub came on right away! Jeez. Shoulda tried that a long time ago.
Yup.
I also turned the freq contol on the plate to "on" and set it to 60 hz. Does that seem correct?
I'm not certain what this does on Hsu Subs. Perhaps someone else can chime in...
Also, another question about my RZ50 levels. I changed the sub out to 0 db. But the fronts are at -12 db and the center at -7. Does that seem right? Or shall I run AccuEQ again?
I would definitely recommend turning the Sub gain up a bit and re-running AccuEQ.
You still have the situation I described above in that your Front 3 are considered to be very sensitive Speakers... With your Mains at -12dB, I don't know if they are maxing out the AVR Trim levels or not. (Some manufacturers equipment is limits the boost/cut range, and some are ±12dB iirc...)
This is why I suggested checking out even just an SPL app for your phone to get an idea of what they are actually doing.
Assuming they are dialed in properly by room correction and your L/R Speakers are each outputting the same level as your Center, then they are good... You just need to get that Subwoofer level set properly. Upping the gain a little should result in getting your Sub down to around -7 - -5dB which is where most systems seem to operate in an ideal setting.
Cutting output costs your system nothing and gives room to boost some where necessary... but if you are already in positive Trim territory, you have little-to-no headroom for boosting when necessary as your room correction may need for balancing the in-room FR.
If it were me, I'd say turn gain to ~1/3 (I think you said last it was ~1/4?) and run AccuEQ again. See where the Sub lands in the AVR's Trim levels.
Then check to make certain your Subwoofer still turns on with the Music Sense feature.
Assuming your Sub Levels in the AVR drop a little and give you more headroom, and your Sub still turns on reliably when it gets a signal, it would seem you accomplish all the goal for a solid setup!