Hi Mark. Assuming you do mean SOUNDS and not STYLES for which latter there is a button the left hand side, I am guessing that the 'saved custom sounds that are filed' as you put it are actually in sound group button MEMORY. (oh yes you said so earlier doh)
When playing The Shadows Apache I get a rather special guitar a la Hank Marvin...I wanted to use this guitar sound for other Shadows music and was able first to load Apache including that special sound and then load another style for another song BUT not load that Style's SOUND over the top of the special Hank sound by using pages 2 and 3 when loading the second style.
More details if this is the sort of thing you are trying to achieve.
Rog