I have a question regarding TotalMix. I've been trying to figure out how to do this, but haven't had any luck. 

Sometimes, when it's late at night, I practice playing bass guitar with headphones instead of my bass amp. But in TotalMix, I can't seem to get the mix right. The bass volume is way too quiet, while the computer's volume is way too loud in contrast.

If I try to lower the volume of the computer (the music I'm playing along with, usually a transcribing software, or YT video) and raise the volume of my headphone, I can get them to balance better, but then if any other sound (such as computer system sound, web browser audio) comes on, it'll be extremely loud because I turned the volume way up to hear the bass better.

I already have the instrument input at optimal level just before clipping (when I slap my bass hard), so can't raise the gain any more. If I lower the software playback, it lowers the volume for everything, including my bass. 

When I used Focusrite Scarlett, I could use its Focusrite Control software to lower the volume of the software (DAW) playback, which is basically all of my computer's sound, including music being played, and then raise the volume of the analogue input for my bass, and achieve a perfect balance. I'd be surprised if TotalMix can't do the same, but I can't figure out how to do it the way I used to with Focusrite Control.

Do you have any advice on how I'm supposed to achieve a perfect balance of my bass guitar and the rest of my computer's audio?