Is there a way to solo 1 channel of the master 5.1 buss? For example if i wanted to solo just the LF channel....without some complicated advanced bussing procedure
A couple of complex bus routing schemes could do this, but not easily.
The best solution would be hardware dependent. If you have an audio card that has its own mixer - i.e. Layla, MOTU, etc - you could mute/solo the hardware channels directly.
Something I will definitely add to the list of simple and usefull.
In the meantime, open up the 5.1 location editor and click on each of the speaker icons to turn them off. Then click on each one individual to "solo". Its "none<->solo" rather than "all<->solo", but its simple.
Now, unless I've completely mistaken your request: Simply turn down the 5 other channels. If you need a right or left channel, unlock it's stereo link located below the fader.