Ok, i'll do my best to reply (optimism_'s too tired or something
).
The sounds are the same for any account that logs on, unless the Audiator directory changes between logons (which it wont unless you change it yourself).
The next version of Audiator (currently 2 weeks behind schedule) will have a user-dependant database of sounds, so i hear, which may affect it.
No doubt a bit of registry modification could get round it tho
So basically, yes, if you added /x99 on your account it would also appear on his account, at least until AudiatorV2 is released.