I own an HD500 and getting a Sansa clip tomorrow. If I can remember, I'll post my impressions here. For the record, the JVC is the best sounding player I have ever heard period. Including Iaudio X5, Sony 818, various Samsung, iRiver ifp 140 and 899..(never heard an iMOD though)
They're very different players functionally though... JVC much larger, clip has voice recording and fm tuner. Hard drive vs. flash. Dock with line-out on JVC, no dock for the Sansa.