Hi Imai
Thanks for downloading trakAxPC. In the current version of trakAxPC, we only offer rendering an AVI in an uncompressed file, thus resulting in your file being a much larger file than the original mix. We will be offering AVI with different compression options in the next version of trakAxPC which will be coming very soon. You can render the mix in WMV which will bring the file size down a great deal.
I hope this helps and if you have any more questions, please do not hesitate to contact me.
Best regards
Cormac