Okay, my setup has been the following when playing live shows with my band.

I play the M-audio keystation 49e which is hooked up through the USB of my PowerBook G4. I ues software such as Reason and Miroslav Philharmonik as my sounds. THEN I use the the headphone out to a keyboard amp(with a 1/4 inch to 1/4 inch jacks cord that has a 1/8 converter so that I can plug it into my headphones OUT on my Powerbook.

This setup ain't working for me. When I play most instruments(piano, harpsichord, etc), the lower keys are so much louder than the higher keys that I cannot concentrate on performance. Instead I am riding the volume levels.

How I can fix this? I only have a headphones out jack as an out on the Powerbook G4 and it isn't delivering stable levels to my amp.

I also own a Tascam US-122 which I use with guitar stuff, but haven't figured out if it could help me send the signal from my computer to an amp in a better way. I am really frustrated.

Aloha look at this Alesis Multimix 8 USB http://www.sweetwater.com/store/detail/MultiMix8USB/

If you really are getting uneven levels (rather than uneven frequency response from the amp), run the H/P output through a compressor before it hits the amp. If its an eq issue then run it through a cheap graphic eq. In either case, I'd recommend looking at Behringer gear - its not the nicest, but its very cheap.

One thought I had while typing the above, as the H/P out is stereo and your keyboard amp is probably mono, have you checked which side of the stereo signal is hitting the amp? If the instrument you play has a wide stereo spread and the amp is only getting the left channel then the bass notes will have much more weight. Ideally, you should get a cable made up that takes the tip and ring from the mini-jack and combines them both on the tip of the mono jack at the other end. Alternatively, you may be able to edit your software instruments to remove stereo panning.

As you are using the phono output of your laptop (stereo 1/8 inch) it sounds to me as if only one channel is heard on your amp. If you're using a stereo jack to jack cable your amp (which I assume has a mono input) will not make contact with one of the channels. I would try to get or solder you own cable connecting the cables of the tip and ring of the 1/8 inch jack onto the tip of the 1/4 jack. Even better and more versatile use a mixer in between.

S