| I believe that head has been discontinued, and replaced by the 409 and 1000 PS heads.
Tonewise, completely different than the Walkabout... huge, deep low end, smooth mids, very hi fi top end that tends to get eaten up a bit in the mix (given my experience with the 502, which is virtually identical sounding to the 600).
Whereas the Walkabout is a bit loose down low but very warm and mid present in the mid-midrange, and a bit old school up top, the PS600 is HUGE down low, very creamy (not punchy.. more smooth) in the mids, and very hi fi pure up top.
It would be a massive, massive tonal change for you. Volume-wise, the PS would be quite louder than the Walkabout into 4ohms. | 
