1/4 connections and XLR connections can both be balanced or unbalanced. Balanced connections require one more conductor/wire then unbalanced connections, that is why you would need a 1/4" TRS (stereo) cable if u wanted a balanced signal. Most XLR are balanced, even though you could technically have an unbalanced XLR signal. When dealing with guitar/bass amp rigs, almost all signals are 1/4" unbalanced, including the guitar signals and the effects loop signals.
The deal is, PA/Mixer/Sound system stuff uses mostly balanced connections cuz balanced lines pick up less noise (especially true over very long distances). Thats why most rack equipment is designed to handle balanced signals. When using rack effects for bass rigs, u should make sure it can accept and send unbalanced signals... Although there won't really be many problems if u used an unbalanced line in a balanced port anyways.
