@Micha
Thanks for explaining how the problems present.

It's clear, from what you say that, TMO doesn't work with the client you like to use (Tapatalk) on iOS and Win8. Maybe that's something that will be resolved in due course, maybe not? Unfortunately, you're going to have to put up with it. However, the more active community members the better, and it would be useful to all if you would post back with anything you can find, so here are a few of ideas to get you going...

Client support
TMO clearly works and can be accessed using many types of browser, so the problem is more a matter of compatibility, on the part of the client you would like to use.
- What was the response you got, when asking this question on the Tapatalk forum?
- This might sound obvious, but have you looked for other clients that might work with TMO, as well as your other boards?

"back end"
At the bottom (of this and every page) there's a link to vBulletin saying v3.8.2 is in use on these boards.
- What information can you find on http://www.vbulletin.com/ or http://www.vbulletin.org , which might relate to the issues that you are experiencing?
- Are there other boards, using the same version of vBulletin that you can access.

Keyboard
My guess is that you don't use your N9 to post/reply is because typing extended pieces on a virtual keyboard (VKB) is difficult and eventually annoying? Long chunks of text it's not really what a VKB is designed for.
- A good solution to this, is to use a Bluetooth keyboard (BTKB) with your N9 and if you want a bigger screen, use the AV out (I have the N900 so cannot advocate a particular KB - sorry). Although not ideal for making replies, while standing on a bus, you can at least type more quickly and comfortably than with the VKB.

I might be completely wrong on all of these and/or you have your own ideas of why things aren't working, as well as how to improve matters. If so, please post the details.