sherry casks is not a problem. if you look in the shulchan oruch (i dont have it in front of me but if you want i will find it for you) it is only nosen ta'am lshvach for wine. for any other liquid wine in the walls of the barrel is nosen ta'am lifgam. when i learnt smicha i was told this clearly by the rosh machon smicha
the problem with this is, is that many scotch experts themselves argue whether or not it is noisain taam lshvach or is it just raicha, which would not be a problem. It is definately not clear whether it is noisain taam lfgam or not. Therefore most authorities say "not recommended" and some will say not allowed if made with sherry casks. I'd ask a rav for particulars...YMMV
(besides why risk it if there are plenty of good scotches on the crc list that are acceptable and quite tasty... i hope i dont get flamed for this)