Big files download problems

hello everybody,
I have a problem with my downloadable products.
I'm using OC 2.3.0.2

I sell big downloadable files,that I have to split in several .rar smaller files (700mb each).
These are the problems :

The main problem is that when a customer try to download a file, before the download process begin pass several seconds or even minutes. The bigger the file , more time you have to wait before the download process begin...
I tried to upload the same file via ftp on my website and I downloaded it with chrome and the download start immediately after i write the link in chrome.
So why OC have this delay in starting the download process?

Anny suggestion is welcome

Hi claud9,
I have a little extension to bypass these issues:
http://www.opencart.com/index.php?route ... me=artcore
You wouldn't need to upload it first in your admin either nor split it over several parts.
If you want to test it, you can pm me a direct link to a file and I'll add it to my demo store downloads.