will the 404 do a roll? (obviously it will play back a recorded roll, but will it repeat a single drum hit at high speed to simulate a roll a la dnb?)

Double your pattern length and sequence in 1/16th pr 1/32nd notes. So if you wanted a 100bpm pattern make 200bpms and 8bars instead of 4 then place you kicks on the 1 and snares on the 4 and you'll effectively have a 4bar 100bpm pattern with way more space to place your sounds between kick and snare. That's how I do it when I do want to sample a roll from a drum loop.
Only problem here for you is that dnb is usually fast patterns and the 404 only goes up to like 200bpm I think, so that might be limiting but for hip hop which chills in the 80-90 bpm range it works beautifully.

master that sub pad man...for high hats and for drum rolls works extremely well...just tap em both...like 1, sub pad...lol. aslo make some double bass shit...that sub pad is a fucking beast lol

doesn't the sub pad just become whatever pad you hit last?

so there is no "hold" button or sample-fragment looper? shame

Just resample to another pad, loop the sample and adjust the loop length to fit the speed of the roll.

thanks for the tips guys

should be gettin my 404 soon... so stoked!