I am using PHP function virtual() for delivering files by Apache 2.2 (it really works faster than readfile()) and that i can check user access permissions.

But can there be in whatever way to include continuous download support, with HTTP_RANGE?

I've attempted such things as this

if(isset($_SERVER['HTTP_RANGE']))  else 

So web-client was downloaded files like if HTTP_RANGE works, however in real Apache just transmits always exactly the same file-ranges like: if client request 4000-6000 bytes, Apache transmits -2000 and etc, so files was damaged.

I believe that there's some method of doing it using apache_setenv, but aren't able to find in the search engines any suggestion about this.

Use xfilesend module for Apache.