The MS-8 can do what you want. My temp setup is a 21inch subwoofer and my stock bose setup running on a ms-8. For setup, keep your sub gain DOWN. Keep it where it all blends ok and on the input setup, when you test each output, the noise coming from sub shouldn't be louder than anything else. Once the MS-8 has done it's thing, you can turn always up it. The MS-8 has a subwoofer control, just make sure when you did the initial setup, the bass knob was all the way down, hu wherever you normally run it and the amp was as high as it needed to be to get you to blend. Then when you want more bass, kick up the ms-8 subwoofer or just go straight for the remote gain knob. The MS-8 won't register that increase, so no, it won't try to keep your bass blending, but at 150db, it's not going to succeed anyway and that's not the point lol.
I don't have a remote knob in my setup, I keep the bass setting and subwoofer at middle positionto get the midbass required that I used for my setup, and simply max out subwoofer and kick the bass setting up a notch or two from there if I'm playing rap. That is enough to max out my subwoofers actual output on a 1000 watt amp. That's pretty good amount of gain built in considering at flat on both it matches up to stock 5.25 midbasses lol.
FWIW, the ms-8 does a "good" job tuning. You'll stil want to tweak it once it's done it's thing, but it does do a nice job, especially if your car has a center channel, or if you willing to add one. Best auto-tune I've heard to date.
Also you can get the MS-8 off of
amazon for less than 500.
Also if you want a setup that blends and another that doesn't you do that by using the favorites, you can set up to 5 presets. Adjusting the bass and subwoofer controls works. However, a remote gain knob would do the same thing really , IMO better. Just turn you SQ setting up on the sub amp lol.l