Can you first try them on someone's receiver or integrated amp? It might be that the faint volume you have there is the drivers themselves having lost charge. Eliminate that possibility cheaply for yourself before spending $ needlessly.
If the drivers seem fine after trying another receiver/amp, then you know for sure.
Also if at that point you are still not too happy with the sound you can possibly bypass the transformers in the cups (transformers should be in the cup rears there behind drivers ...) and rewire them with a Stax electret cable and run them off a Stax adaptor box ( or rewire to a box of your choice so long as the cable plug end fits the particular adaptor box.)
, but you'll lose portability obviously with no more TRS jack.
Good luck
These being a " Back electret " they use a slightly different setup for what has the permanent charge embedded , but I am sure this was mentioned.
http://wiki.faust3d.com/wiki/index.php?title=Electret_Driver_Principle
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