Here are my SF-2 settings. When you plug your input into channel A and your output is from channel B, you have, essentially, a 3 channel mixer. The three channels are parallel and are combined at the output.
The knob to the left, the input gain, is, in this configuaration, the master volume; and I leave it maxed.
The first filter I have set for low pass. I pretty much always leave the frequency setting where it is in the pic and the damping ratio all the way down. I adjust the filter gain depending on the room I'm in and the cabs I'm using. A typical adjustment might be from 4 to 5. These setting give me a nice broad and even low end.
The second filter I have set for high pass. Again, I pretty much always leave the frequency setting where it is in the pic and the damping ratio at 1.5. And again, I adjust the filter gain depending on the room and cabs. A typical adjustment here might be from 7 to 6. These settings give me a broad and even high end.
The direct gain knob is the third channel and is the dry signal. I also adjust this setting depending on the room and cabs. A typical adjustment here might be from 6 to 7 and is often made in conjunction with an opposite adjustment to the high pass filter gain. For instance, going from 6 to 6.5 on the direct gain and at the same time from 7 to 6.5 on the high pass filter can make a big difference in the sound. Adding more direct gain and backing off the gains on the low pass and high pass channels will of course give me more mid range punch.
These settings work with all my Alembics. Note however, that my sound has very little in the way of growl or low-mid punch; it is very clean with clear low end and a lot of broad high end. I would imagine that my sound is not what most players are after.
Don't let yourself become frustrated. It can take a long time to get used to the SF-2; but learning how to use it can be fun. It took me a while to get to the settings that I use; but fortunatley for me, I enjoy practicing.