If you want to spend $600, then by all means, go for the JL. I could also recommend a PPI-PCX480, a PG 600.4, avionixx 440.4, TRU T-4100 v2, ARC CXL 4150, among others. MTX, alpine, and RF make nice amps, I know because my MTX was underrated by about 50%. But depending on his budget, he might...