I have had a JBL 4638 for about a year now. In December I got the SVS-2039PC+. Before I got the SVS I was planning on getting rid of the JBL, but when I heard them together I decided to keep both. The JBL has plenty of punch, but of course can't match the SVS on the lowest frequencies. As stated before the SVS is awesome for movies, giving low frequency, wall shaking SPL with no problem. The SVS does good on music, but much better with movies. I think that is more of a factor of the frequencies of the music.
The JBL can put out some awesome punch on music. Playing "Creeds" What If, the JBL 4638 rocks my whole house.
The rest of my speakers ares Klipsch KLF-30's, KLFC-7 and JBL rears.
Benny