thrasherIf you are looking for concerts, the big main concert venues in the city are:
The Trocadero
www.thetroc.com
10th & Arch
(Chinatown)
The Electric Factory
www.electricfactory.info
421 N. 7th st.
The TLA
www.tlaphilly.com
334 South st.
(Very popular street. Lots of bars and stuff.)
The Tower Theatre is technically in upper darby, and you obviously already looked into that one. If I were you I'd check out the other venues for upcoming shows.
I looked through the calenders of all 3 of those (plus Philly Union, Tower, Johnny Brenda's, First Unitarian Church, Barbary and a few other bar/smaller venues in the area) and of all of those, the only thing decent (imo) that coincides with GXL is the Porter Robinson concert. Obviously, everyone has their own taste and could go to a different show, but I thought it notable to post the Porter Robinson show due to this communities love affair with Lemaitre.