That works. I now have root access with telnet. Let's see what kind of damage I can do to Twonky...
I found the clients.db file in TwonkyVision/resources, copied it to a shared folder, changed the file permissions, copied it to my PC for editing (with a Unix-compatible text editor), made the recommended changes, copied it back to the resources folder, and restarted the NAS. Now I can stream mp4 video (only if the files are named m4v for some reason) and mpeg video files as well as avi, pause, skip forward/back, go to time index. Big improvement! No luck with mkv so far - everyone says Twonky doesn't support mkv, but it looks like people have had some limited success by spoofing the MIME type in the clients.db file as long as the DLNA client supports mkv.
Thanks for the really useful help here on this site and in this forum.
Update on mkv and mp4 video file support between Twonky on the NAS and my Samsung BD-C5500 Blu-Ray client:
I read everything I could find on other people's experiments and tried a bunch of my own, without success.
No luck with mkv. Darn! Most of my DVD rips are Handbrake H264 mkv, and play just fine on the Samsung player from a local USB drive. Twonky seems to recognize the mkv file type as video, but will not stream it successfully to the Samsung with any combination of different mkv variations produced by different programs from different source media with any of the suggested mime types. I tried dozens of variations. Some produced different behavior, and sometimes it looked like the Samsung was really trying to start playing the stream. In some cases it looked like it thought it actually had played the video. But in the end, no video with any of them. Some people have claimed partial success, but without providing details, and they may have been using Twonky 6 running on a PC.
Also no luck with mp4, although m4v works. Most of my "mp4" files were actually generated as m4v files, and will play on anything that plays mp4 files, whether named as m4v or mp4 (including my iPod Touch and my HP TouchPad as well as the Samsung Blu-Ray from a local drive). Twonky will stream them successfully to the Samsung Blu-Ray player if they are named m4v, but not if they are named mp4. I tried generating some test files in iPad mp4 format from various programs, and none of them worked with Twonky/Samsung combination. Either Twonky didn't like the mp4 format and refused to see the file as video at all, or it would not stream successfully to the Samsung (although it would stream to others like the iPod Touch, and would play on the Samsung from local storage).
Do you ever get the feeling that DLNA isn't much of a standard?