The difference between the versions may be non-existent since I didn't have the EMI for a while and couldn't test it then.
I tried my Audiowerk8 - it just crackles, no matter what buffer size I set it to. This is probably unrelated and I don't care too much since I rarely use it any more because of the better audio quality of the EMI.
Just retried the EMI - set the buffer size to 512 (256 before) - now it plays for some time (some minutes before the dreaded -224). Switching it to "output only mode" the error didn't occur yet.
I coudn't use the built-in audio like you suggested - there's only some multimedia-speakers connected to it for system sounds. My EMI and Audiowerk are connected to my Mackie 1402 mixer though, together with Virus C, Yammy DX 200 and Alesis QSR for sounds.
I won't change this setup because of a software bug

- which I'm quite sure it is, since the EMI works flawlessly in e.g. Rax0.3.3b, where I also tested the Reaktor 4 VSTi. And it works with lots of audio tracks in OS9 with Logic Silver 4.8.1.
Another GUI-bug I just noticed while testing: If there are only audio tracks in a freshly opened file the zoom buttons (+,-) in the track window don't work - they are greyed out. The only way to get them working is by entering some midi-notes on a track.
And while I'm at it - on startup I always get a vertical scroll bar in the Graphic Editor but can't resize the window to make it disappear, though there's plenty of room below it (my Dock is on the left of the screen, hidden while I'm in Metro). A workaround is to alt-click the "+"-magnifier, then resize the window and then alt-click the "-"-magnifier. Seems there's only a few pixels missing in the default height of the Graphic Editor window.
Thanks for trying to help, Achim.