Subgrouping Muenchian Grouping

Right now I'm using the Muenchian method to group together albums from a
straight playlist xml file, http://sysrq.tk/code/muine/playlist.xml ,
the XSL file is http://sysrq.tk/code/muine/group-albums.xsl and output
is at http://sysrq.tk/code/muine/group-albums.html . My hasn't occured
to me until recently when I purchased an album that is the same name as
one I already owned, now both are grouped under the same album, I was
wondering if there was a way that I could again seperate the albums by
artists, I'm just not sure how to go about this in XSL. Thanks.