The 8060 is definitely quieter of the two. The hiss seems high, I'm wondering what level changes exist outside of the 45dB gain you mention, maybe a youtube gain adjustment. My MKH105, MKH406, MKH30, and MKH800Twin are much quieter at 45dB into a vintage tube preamp from the 1940's, which has its own hiss contribution, and I record fairly quiet classical guitar performance with those. Are you recording loud live shows, and they still do not overcome and mask the hiss? To ask the dumb questions (I don't know the MixPre-6), all pads are turned off, and no limiter is engaged? I know my DR-701D limiter automatically increases the hiss level quite dramatically. What is the sound comparison?