The tone on the 604 sounds amazing to me.
I remade my soundcloud account just to show you 
This is the bass, clean into my DAI, neutral EQ.
Here it is through an Ampeg preamp I used to have, to give you an idea of what it might sound like through an amp:
As @terb said, bright attack, punchy low mids, higher mids a little scooped sounding. I really like the sound.
Go to a store and try them both!