Excellent!

Chunk size, read ahead and so are not configureable on the command line yet but given the confirmation that the command line works and the platform it runs on I'll do something about it. That is not 'java stuff', but application specific stuff.
You should know that BT747 always downloads in multiples of 64kB which is normally your case since the memory was filled with about 1kB. So you took about 17 seconds to get 64k. That is actually not to bad for bluetoth - I did not get to do better than 2k/s on my Nokia phone using the J2ME version.

Did you have to do anything to install the RXTX binaries on Maemo?

Regarding the GUI. The error is reported in one of the libraries. I can go and guess why and possibly do something about it. The other solution would be to simplify the GUI and use more 'basic' Java library stuff. Of course, if the normal GUI can work, this is surely better.

If I can not do something about it easily, I can catch the error and avoid the program from stopping - parts of the GUI will not work, but at least there is an estimate of how much that is. It may require some back and forth to update the builds.