It looks as if I was wrong...

[Bound2Burst]

The problem with downloads does not rest with OpenCart, but with Apache which limits the size of files that may be downloaded. In the past this was seldom a problem because most files were well below 2 GB, many below 1 GB, so the situation rarely arose. Now, of course, many files exceed this limit.

I'm not sure where Dreamhost has the limit set, but I have asked them to increase it to 3 GB per file. Hopefully they will okay with that. It still means simultaneous downloads are not a good idea; unlike most stuff that you download from the web, these files are huge and it can cause problems, so before you set those multiple downloads going, just have a think.