i have a usb guitar and need the speakers to hear the effects Guitar Rig/amplitube put out.
They are a top quality speaker the Logitech's....which is why i would like them to work with either laptop i'll be buying
Guess I'm a bit of an audiophile. I used to think Logitech and Bose speakers, and other such basic speakers, were super high quality and nice. Once you get into it, and you demo some nicer speakers (certain Swan speakers, and lots of other brands that require receivers... Energy, some Klipsch speakers, Kef, etc, etc...) you might realize there is a huge difference.
If you've got money, get a receiver, use Thunderbolt-to-HDMI, and get a high quality 2.1 setup. However, that's going to be expensive!!!
To directly answer your question/scenario... the Macbook Air won't be able to output 5.1 sound unless if you have a plug that can plug into the Thunderbolt or USB port, and adapt to whatever is used on the z5500. So I guess you could look at the Pro... though I don't know what extra plugs it would have that would remedy this issue. You may simply need a desktop.
I think there may be external sound cards you can buy that have all the plugs you need. In fact, I'm pretty sure there are. They connect via USB. The one thing I do not know is if these sound cards function on a Mac, or if they're Windows-only. You could google up "USB sound card" and try to find that out. Or possibly someone else knows. If you can get one that will function on a Mac, then you could use an Air for certain.