I understand very well what you've been saying Sheriff and I know enough about computers not to have to resort to a dictionary to see what an interrupt is.
The ONLY proble with your setup is that it has become obsolete. Not in the sense that it does not do the job, but in the sense that you simply can't recommend to anyone "get an Atari and make music" because there wouldn't be a new Atari to be found, the company ceased to exist many years ago, and the user base -strong it was once - is shrinking fast, I believe. This machine, was great, but the problem is that it WAS great, in the past tense.
Today, the only things available are Windows machines, yes Linux is good, but still not for the masses.
I may find interesting and clever enough that your machine reserves a real interrupt for MIDI, but most guys wanting to make music, don't know what it is and they do not care.
They want a thing that will start making music with not much hassle. In that sense, a generic keyboard/computer that can load sounds and styles from various manufacturers as "to the genesys" suggested, is a good deal. A PC with the appropriate software, stripped down from unnecessary programs and threads, will do fine instead, as the Atari used to do. It may still do good for you, but I think that less than 5 people in this forum will have the knowledge and time to invest in a 10 year old machine for making music today.
I really hope you take no offence with the above, it is meant as a comment only.