A hobbyist here, so be nice.

I am unable to make use of the both speakers on previewing the sound recorded through final Vinyl with a guitar.
Only one will work, and both are fine, why?

I am still unfamiliar with mac. I use an iMac g4.

Hi. I am unfamiliar with Vinyl, but maybe I can provide a little insight. I assume you are at least running OS X? If so, check your system preferences...you can open these under the Apple menu---top left...or from your dock. Check the sound output...sometimes the balance controls can go left on their own. Make sure Built-In audio is selected. Hope this may help....

Better still, check your guitar input to make sure it is in stereo. If its just a standard guitar jack or mono cable, you may find that sound is only recorded on the left audio channel. This is a pain in the arse but can be fixed by getting a stereo jack cable (£1.99 from Maplin) make sure that the end of the cable has at least 2 rings around it like a headphone jack.

Hope this makes sence.

that is probably because a guitar is a mono instrument.

lol...
yup.
The only way to record stereo gtr is thru a box like a pod (line 6)....etc.

Thank you all.
The audio jack is mono.
I will get the stereo one.
Thanks. I didn´t know the meaning og the ring.