Does the Sonus Mod address or fix the low end problem with the Uberschall - Yes, the Mod does address the excessive low end to better balance the over all highs, lows & mids. The mids are also corrected & a 'Shift' Switch can be installed on the Gain Channel for an additional $150.00 should you want the option to select between 2 different tonal options. 

Can you make the Clean Channel better - The design of the clean channel is not ideal & as such we have to work around the way the circuit is laid out on the printed circuit board so there is not a lot we can do with the clean channel (just being honest).

I'm using an 808 in front to roll off some low end & make the amp smoother or easier to play, will I still need to use the 808 - No, after the Mod the amp is much easier to play so a pedal is not needed. The amp will still work great with pedals but it's no longer a must to use a pedal in front to smooth up the amp. We also increase the over all natural sustain

The Presence control doesn't seem to do much, does the Mod fix this - Yes we do re-voice the Presence control on the gain channel so that it's more versatile & flexible