Hi, i´m new with my sp404sx, and i have too many questions, but first:
How can I match two loops by pressing pads together (without making a pattern) and keep them syncronized?
I had the same BPM and length in both, but i think the start point it´s a little bit different......it´s posible to fix it right?
I apreciate your help. (sorry for my poor english)

if you resample them on top of each other they should trigger at exactly the same time

use time stretch to match the lengths, then set the sequencer tempo to the same as the loops. then put each one on the sequencer with quanitize and 8.

now they will stay in sync forever, and you can mute one out with isolator, if you want.

Without making a Pattern you must do as Nosmo suggests and resample the 2 pads together. No matter how accurate you get pressing 2 pads at the same time they will always drift as there will always be some amount of inaccuracy in pressing the pads together by hand. By resampling them together you can play them together and they will never drift. You also save on polyphony (unless you make 2 mono-->1 stereo)
C

Thank´s