How to turn on Unity Gain on Pre Amp

Can't find HT bypass mentioned in the owner's manual. Is tone bypass the same thing? below is the section from the manual 

Tone Bypass Press the Front Panel Tone BYPASS Push-button to remove the C2500 Tone Circuitry from the signal path for the currently selected Input Source. The LED above the TONE BYPASS Push-button will illumi�nate. Refer to figure 50. The C2500 remembers for each selected Input whether the Tone Control Circuit�ry is deactivated. To reactivate the Tone Control for the currently selected Input Source press the TONE BYPASS Push-butto

Not the same thing....

Tone bypass is not HT bypass, its function is to deactivate tone control setting.

On the C2500, " Passthru " is HT bypass. To activate passthru, you need to sent a 12Volt single by an external source to the back panel "power control" "Pass-thru" jack via a 3.5mm stereo cable (see owner's manual page 4).

Once the "Passthru" function is activated, all front panel control knobs and buttons including volume control will be deactivated except the "output 1/2 buttoms" (see owner's manual page 25), and the volume level will be automatically set and lock into unity gain (70%?).

I misspoke on the subwoofer being one of the reasons why I need the preamp. It has been a while since I looked behind my gear and the REL subs are taped into the amp, only the grounds are on the preamp. So easily hooked up the Lumin direct taking the preamp out of the system and surprised to say it looks / sounds like a clear winner. Didn't want that to be the case as I love my tube preamp, paid a lot for it, and it has cool blue meters.... Still got some A/B testing to do, but I know my system and every audio adjective there is seems to be noticeably improved. Makes no sense to me??  I guess less is more.