I've made a workaround for this problem.
It's a dll that is usable with mIRCs /dll and $dll(). It rewrites specified music files ID3v2 tags in a (proper) form mIRC is able to read, and thus making /splay of the file possible.
Rewriting tags in middle of script is time consuming, so
I've included a short example of how to use it effectively in mIRC scripts by replacing the default /splay with an alias that only uses the dll when default /splay fails.
The dll along with the sources and documentation is posted on mircscripts.org and is currently waiting for acceptance and review. If you feel like reviewing/checking it out, find "tag.dll (/splay fix)" at
http://www.mircscripts.org/queue.php 
