scene modifiers, cleverly applied to an amp model's drive level and output gain will allow you multiple varieties of clean, mid gain, and high gain tones from one amp, each assigned to a different scene, and gapless. One concern might be the bass/mid/treble/presence settings as the gain settings change, but this is also manageable with EQ blocks engaged/bypassed as needed.
As mentioned previously,
@clarky made a mission of using control modifiers on the AxeFxII with an expression pedal to transition seamlessly from one amp sound to another, with 2 amp blocks.
I also think that AxeFxII with scenes + X/Y, on 2 amp models having parallel signal paths and vol blocks in front of them, can get you up to 4 amp models with seamless switching. I haven't tested this yet but the idea goes like this:
scene 1: vol block engaged row 1, amp 1 X engaged; vol block bypass muted on row 2, amp 2 X engaged
= amp 1X audible
scene 2: vol block bypass muted row 1, amp 1Y engaged; vol block engaged row 2, amp 2 X engaged
= amp 2X audible
scene 3: vol block engaged row 1, amp 1X engaged; vol block bypass muted row 2, amp 2Y engaged
= amp 1Y audible
scene 4: vol block bypass muted row 1, amp 1Y engaged; vol block engaged row 2, amp 2Y engaged
= amp 2Y audible
the thought here is that the bypass/engage states of the volume blocks (that control whether signal does or does not flow to the amp in row 1 or 2 signal path) will switch from row 1 to row 2 quicker than the amp blocks as they change from X to Y state. Similarly, you could assign amp 1 to see Left input and amp 2 to see right input, and use a pan block with a scene modifier to change from L to R per scene as desired.
It's stuff like this that makes the AxeFxII the leader of the pack for routing and control flexibility.
My memory of all this is far from perfect, so feel free to correct or clarify any erroneous information or assumptions I may have made in this post.