"Rise from your grave"
Whilst looking for a Sound Canvas module on our local Facebook marketplace, I came across a Roland SD-35. I tried to find some info on it, but there's hardly any available with regards to DOS gaming, this is pretty much the only post. I did however find a potential solution for the buffer overflow issue, hopefully this'll help others who experience the buffer full message.
SD-35, SB-55: 'bFL' (Buffer Full) Message
In order to record any MIDI information quickly, and/or in massive quantity,
you should turn Soft Thru off. This prevents the SB-55 or SD-35 from trying to
pass the incoming data 'thru' to the MIDI Out port which requires the processor
overload in some cases - depending on the speed and quantity of the data.
1) While holding the SET button, press the left SONG button.
2) Use the REW and FF buttons to change the display to 'oFF.'
3) Press the SET button to finish the operation.
In the end, I found an SC-88 Pro, so I bought that instead.