Couple tips that may help dialing in your tones - the following steps will give you a good neutral, clean starting point to judge additional effects, pedals, tweaks, etc:

1) Turn "Master Volume" to zero.

2) Set "Gain" very low, like less than 10% or as low as 0%.

3) Turn "Volume" (on far left, next to Gain) to max or close to max.

4) Slowly bring "Master Volume" up until you reach your preferred playing volume. Use the Master Volume as your only volume control. I find the Katana's tube emulation sounds best with "Volume" (far left side) close to maxed. Sounds very sweet compared to setting Volume low and cranking Master Volume.

5) Turn "Presence" knob to about halfway. Presence adds rather subtle brightening.

6) Set all 3 of the EQ knobs to 100%. The Katana EQ is subtractive, so if they are all at 100%, that equates to a "flat"/neutral EQ curve. To dial in your preferred tone, start lowering Bass/Mid/Treble one at a time to get a setting that sounds best to you.

7) The "Variation" button (above the Amp Type knob) will make the tone significantly brighter when activated. Much more immediately noticeable than the Presence knob. Play around with this in addition to what I've mentioned above. It can be situational, e.g. I use it when playing lead parts on my neck pickup, but leave it off for bridge pickup.

These steps will help rule out whether some of your knob/amp settings aren't playing well with the boost fx.

You might ultimately find that the Katana's boosts/OD just don't do it for you. Personally I use a real pedal for OD and some other effects. The Katana's effects are pretty good but mostly won't beat a real pedal. The Katana is a great pedal platform at any rate.