I have no solution for the distance problem, but if your computer has a sound card with a line-in plug, you can connect the cassette output of your amplifier to this line-in. You then need some software to "grab" the incoming audio. AudioGrabber is really good for this and free.
Otherwise you might consider a turntable with USB that you can connect to any computer, but this costs about $100
I want to convert my lp 78's to cd format. I have Roxio creator 9.0 de, but I believe i have to upgrade to roxio creator 9 to get the correct soft ware. I have JVC stereo and a vostro 200 dell computer. One main problem is the computer is not close to the stereo. I would say i need a 10-20 foot connection to get them connected. I'm guessing an adapter cable that long would be very expenzive, and since I'm an old guy on social security I need all the help I can get.
The computer is on an outside wall and the stereo equipment is on an adjacent wall.
Old Dino Man