i would only ever use normal amiga 4-channel MEDs in anything i do anyway. i enjoy working to the limitation, and feel you need a really good amiga to get anything listenable out of the multi-channel modes.
the med library i have must be the one from Soundstudio, and i can always send you that if its needed? (that would support MMD2) - but i would bet good money on the one in the octamed 6 demo being fine.
i never did find a solution to closing the MED library in AMOS. i have worked around it now by converting my wanted MED to MOD, but its not preferable, as AMOS doesnt seem to pick up command-line tempo settings properly, chosing to play all my tunes too slow. I over-cranked up the tempo in protracker, and it seems to act as a crude work-around! sadly, this woudnt work well for anything which was loop-based, as that would be very tempo-specific.