Well I like your thinking - program change would be a good way of selecting 404 patterns - but it doesn't do it I'm afraid.

If you're prepared to play with a complete backing - a 404SX SD card (2 gig would be about right) could hold more than enough for a gig. Yes, you can record a complete backing track for each song as samples on the 404 pads. With both Gate and Loop settings off, the 404 will play thru just once for the one pad press.
You won't have footswitch control - well... an FCB1010 pedal can send midi notes which will trigger a 404 pad (playing the sample on the pad), but if you hit the wrong one... I think that would be too easily done with a foot pedal.

Incidentally, the way to stop the 404 playing a sample in an emergency is to hit it's Cancel button 4 times - it doesn't have an instant stop button. Probably safer to turn the volume off first. So you'd need to be careful not to make embarrassing mistakes at a gig!

Actually, as a backing machine is a cool use for a 404 even though it's wasting a lot of it's features. There aren't many other things that can do it - with a separate pad to pick any song - for the money. The sampling and FX can still be used in creating the backing, and you could fool around with the FX during instrumental sections.

Jim

So I think I may have been over-thinking things. All I want to do is play 404 pattern in sync with my drum machine. I'll have to switch patterns with my hands, but when I think about it, it's not really that big of a deal. That's possible right? Or is that where the SR-16's polyphony comes into play?