Sorry, I wasn't meaning to be assumptuous. I'm just trying to help.
I'm just used to using hosting providers that let you host whatever kind of files you want on their servers (within reason). I've used a couple of dozen such services over the years. They all work very much the same way and will almost certainly allow you to store your json files. I gave you a couple of examples, one that's known to be fairly reliable, but you have to pay for (although there's the 45-day money-back guarantee), and the other that's free, which I've been using for several years since they started, with only one major issue that whole time.
Amazon S3 sounds like it should be a good solution for what you want to do, especially if you're already using it and paying for it.
I thought you were on track with getting your feed working on S3. Initially, the file was not being served with the correct Content-Type header, but you said you figured that part out. Then you said you were having further problems with strange characters at the start of the file. You never responded to the questions I asked you to try and diagnose the problem regarding how you were creating the file and whether there's anywhere you can specify the character encoding.
Then you said you couldn't get your feed working even if you hosted it on myjson.com, which would indicate the problem wasn't with S3 at all, but with the feed. Then you said you found errors related to "the content object does not seem to conform to the specs", but which were actually a bug in the script you wrote to generate the Json file. Again, problems with your feed, not with your host. Now you say you have another web site associated with your channel. That would seem to be a logical place to host your feed. Yet you say, "I can't get the content type correct when I try to ftp it". Well, you don't normally set the Content-Type when you ftp to server. You configure the server to set the Content-Type when it serves particular file types to the client. S3 is a little different because of the way it sets up its "buckets".
Basically, you're going round in circles here. I would go back to square one if I were you and start working with a known, valid, JSON feed file, so you can rule out any problems with the feed itself or its encoding. My recommendation would be to set up a test private DP channel by following the Roku
tutorial step-by-step - exactly. Use the feed file they supply and put it somewhere (start with myjson.com, then try your own web site, then try S3). That feed is known to work so if you get the same errors as you're getting now, then we've eliminated the feed as the problem, and can narrow it down to what's going on with your hosting.