Wow, how epic!! I have the memory expansion board in my EX (With the DMA controller) so now want to try this out too in non PIO mode. I'm lucky enough to have the Tandy serial card in mine for some hot "mouse" action. I was given the whole setup by someone here who was about to throw it away since the computer wasn't working.
Had you seen my video (posted just the other day) about using a floppy emulator to get 2.5mb floppy images on the Tandy 1000 EX? I used a $17 USD Gotek with 10 euro HxC firmware. Also there is a video about using a 3.5" floppy internally on the EX. (Any 3.5" HD drive will do. The cable needs a small modification.)
I had to replace one IC on my EX to get it working and I Found a source for Tandy parts in the UK that pretty much has everything. They bought the entire stock of Tandy UK parts when they closed up shop in the 90s and seem to have everything on hand.
They likely have the DMA chip required to build a new memory expansion board with the DMA controller.
Autogard UK:
http://www.autogarduk.com/I was working with Martyn there, email address: SALES@autogard.freeserve.co.uk
Tandy 1000 EX floppy emulator video:
(other 1000 EX videos on my channel too like the repair video and CPU/floppy replacement video.)