most likely, your audio card can't cope...if u have a keyboard try playing some cords, if u dont hear all notes then its prolly your sound card. i had the exact problem, as soon as like 5 instruments with real full would kick in sound they would mess other samples up, i have it far less now ive got a real good sound card (konnekt 8
from tc electronics) also what might help is to use some filters...filter the sounds u dont need from the samples, make sure u r not clipping, pan on samples slightly right and the other left. first of all make sure u dont get the master audio in the red, use the m-class mastering stuff to beef up the sound again when you are ready to record. after spending like 5 years with reason nowi can give u one huge tip....go for the good sound card before you go for any other upgrades (especially dont go out and buy monitors if u still use a non-professional audio-card) if u want a good audio card dont make the mistake some people do and buy an expensive soundblaster card, it might improve your sound but its ment for games,l not recording audio...i think the konnekt-8
is a great card, its easily the best in its price class (real nice warm sounds) i had an firewire-solo card too. but it was so damn bugged i had to either reinstall the software everytime i wanted to use it or do other weird stuff in order to get it to work so i can recommend that one.( after 2 days, i ran back to the store and paid $100 more for this card which hasnt let me down yet...
(btw its not suited to play games with...it lags them up, so i use the crappy card for that :P)
hope this was of some help...if u have a crap card (like realtech ac97) u can try downloading asio4all
driver to improve latency's and stuff
have fun in reason, its a great program....but u have to work pretty hard to get those really full sounding wav's....i am still elarning tricks everyday and i've been using reason on and off for like 5 years now.
ps i typed this kinda fast, and i cant really type well, on top of that i am lazy so now u know why this text is full of spelling errors and pretty crappy in general cheers!