Go to your Xtreme program filters folder and kill the old HTMLfilter.dll by naming it htmlfilter-dll.OLD
Copy Covoxers latest update of the HTMLfilter.dll

Restart the computer - restart Xtreme.
Nothing should prevent the new HTMLfilter.dll being used now.

I've had to reload it each time I need to export my HTML otherwise it shows images as PNG's with names of img="http...../etc."
I don't fully understand what you are saying there?

Using Johns method works fine for me:
To insert external image you have to create a placeholder object (with correct size and positioning). Then add a name to it:
img="http://www.myimages.com/image.jpg"
That's it. Entered link will be used in the exported html.