How to turn on Unity Gain on Pre Amp

thanks for input all, i’ll check HT bypass. I am running dual subs so eliminating the pre is not a great option. at this point i’m wanting get the best test i can with the leedh with preamp in place and see what i hear. I can’t help it go down the rabbit hole a bit but the truth of the matter is I would prefer to maintain using my preamplifiers remote control as opposed to the iPad through the lumin app or roon app. if I like what I heard I can investigate the LUMIN remote but I’m not sure how that would integrate with and everything though?

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

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.

I am only streaming so the preamp really only serves as a sound conditioner and volume control. I am a Mac fan and have auditioned other brands and settled on Mac. I do believe in my case that less is more vs some other preamp option. I wouldn't be surprised if some ultra-expensive preamp performed better than c2500 but I have no interest in going down that road. It sounded great with the c2500 and now seemingly better direct from the S1. Further listing tests on that is yet to be done.

OK I feel like a bit of an idiot..  just goes to show in the hi-fi world psychosomatic pre-expectations can be real.. I put the preamp back and it sounds every bit as good maybe even better than without.. crazy, I know i was convinced that it was better without it when I first took it out. i do have the leedh volume turned on but experimenting with the unity game at 70% on the preamp and going back-and-forth using the preamps volume not hearing much a difference either but the leedh is on the entire time which I think is a good thing.