Unable to download files with http profile assigned to VS

The idea would be to simply disable the HTTP profile (put it in "passthrough" mode) for specific conditions. Take a look at the following article for handling webdav:

https://devcentral.f5.com/wiki/iRules.DisablingHTTPProcessingForUnrecognizedHTTPMethods.ashx

And the iRule:

when CLIENT_ACCEPTED {
     Enable HTTP processing for all requests by default
    HTTP::enable
}
when HTTP_REQUEST {
     selectively disable HTTP processing for specific request methods
    switch [HTTP::method] {
        "MOVE" -
        "COPY" -
        "LOCK" -
        "UNLOCK" -
        "PROPFIND" -
        "PROPPATCH" -
        "MKCOL" { HTTP::disable }
    }
}

So if you can distinguish the download request from other requests, you should be able to do similar.