Okay.... I've gotten the TED sound playing the main theme, although its been a bit of a nightmare.... it turns out that normally these operate at location $D400 - the original location of the SID on the C64. But add-on for the plus/4 is mapped to $fd40 (or $fe80), but when the card isn't there then this is just normal IO space - and theres no RAM there. This means it just doesn't work! What I've ended up doing is making a relocate routine that runs through SID music player and then moves the writes to the SID card to an area of memory the Frequency convertor can get access to. I've also managed to shrink it down by 50 bytes, but I've had to add the relocate routine... so I've uised up just over 1k for this.
However....now for the REALLY bad news! This routine takes around 16 scan lines to run, and thats on top of the SID player! This is very painful! So, if we run low on memory again, this is the first to go as it will slow the game down in busy areas.
Still, I've given Luca the mconv source and he can release it on +4 world at somepoint so others can use it. As I said earlier, the source lets you play around with it easier..... as well as relocate it and change the storage locations.