Instrument layering in Gigastudio is the ability to layer multiple instruments (all with independent volume/pan/etc controls) to a single MIDI channel. So if I have two different Violin I Legato instruments from two different libraries, for example, I can mix them together on the same channel to make them sound fuller or bring out the strengths/minimize the weaknesses of each. Works really well with staccato samples, as I have one library with alternating up/down strokes and another with straight samples. Layering the straight samples helps to tone down the (somewhat obvious) up/down stroke sounds, while still mostly avoiding the machine-gun effect the straight samples would produce on their own.'Instrument layering' I don't know what that is (I'm not a Gigastudio user) so can't help there.
I'll give the reverb you suggested a try as well, once I get the other stuff running. Thanks!