Hi Laska!
I've got an 800b that I sometimes experiment with. I don't need it for anything in the near future, so I haven't arrived at a final solution yet, but amongst the mods I have tried are replacing the preamp section with an INA 217, and also eliminating all the electrolytic caps by using DC servos instead. A lot of hassle, and certainly not something I'm going to do on all channels, but it did have much better LF response. It also oscillated with maximum LF boost, but that's just because my servo design skills are shit! Anyway, I would go with all that Jakob recommends, in particular a larger cap for C6, as that is where you get the greatest amount of LF 'wooliness'. Don't forget that this is an old desk; I think mine is 20 years or more. Soundcraft no longer carry spare pots. I have thought of mods that would cost up to 50 pounds per channel, which would be pure folly to implement. Realistically, I shouldn't spend more that 10 pounds per channel at most. You have to consider how much use you will get out of this desk, and how long it will last before maintenance gets unbearable. Having said that, I replaced all the faders on mine, and so far none of the pots have given me any trouble...I'll keep my fingers crossed!
Bjorn