from the 2 amazon reviews the one guy said he went to go replace his MB
QP-240 but they had changed companies over so the new version of that was the
GMP 240.
Maybe searching through the QP-240 threads will give some insight besides the two reviews here.
http://www.amazon.com/exec/obidos/ASIN/B002LVUKE2/bestseller-headphones-20
QP-240 search results
http://www.head-fi.org/newsearch?search=QP-240 I might do some reading myself
Are the old version also 100 ohms i don't know.
looks like the MB QP 240 are 100 ohms x 2
have a peek at the catalog if you want, though I have no clue if they are indeed exactly the same.
Specs are on the picture at the bottom titled " MB Quart 1995 Brochure p5 ' click to expand a couple times
http://wiki.faust3d.com/wiki/index.php?title=PMB_/_MB_Quart
also all the available Peerles/MB/Quart?gmp whatever is complied nicely here in this massive chart.
http://wiki.faust3d.com/wiki/index.php?title=TalkMB_/_MB_Quart
( from the above link =
"Available specs appear identical to July 1997-era QP 220."
It's technical stuff yeah but it might help you figure out if it is the same then you can see if the build is similar then possibly use other impressions from the older model as a baseline.
I dunno it's fun though.