Audio Systems: Audio input/output with a laptop and a receiver, headphone adapter, audio sampling

Question
I have a pair of related questions regarding audio on my Apple MacBook. Aside from the laptop, I have a Yamaha AVX-100U stereo amplifier, a dime-store guitar, and a variety of cords (most ending in 3.5mm jacks).

My questions are:
1.) How should I connect the laptop to the receiver to get the best sound from the speakers or a pair of headphones? Right now, I have all relevant digital volume controls (system volume, iTunes, video player, etc.) maxed out, as well as the system's audio sampling rate (92000 khz or whatever it is... a lot higher than the standard CD sample rate). I use the line-out/headphone jack on the laptop to connect to the receiver and control volume exclusively with the receiver. Is this as good as it gets?

and...

2.) I screw around with some music software (Garageband and Ableton) and sometimes I use a guitar. The problem I'm having is that I don't have a proper cable--I use a 3.5mm-to-3.5mm audio cable with a 3.5mm jack in the laptop's line-in and the other end plugged into the guitar with a 1/4-inch headphone adapter. Garageband will only record guitar tracks in mono with this configuration. Is this easily fixable? In either case, what is the best way to get guitar tracks onto my laptop?

Thanks a lot for any help.

Answer
M box is one option. Made to work with Pro-tools and can be configured for Garage band. It is an external device and has a high quality DAC. The sound reproduction should certainly meet the quality of the source file. At this point the M box will provide you with balanced inputs and outputs for any pro or semi pro recording. It is a tool used by many pro musicians. If you want to get professional results you need to match the I/O connectors of the audio equipment you are using. No 3.5mm connectors have pro capabilities.