I think it's really just a come-on to sell the XK basses which are Korean or Chinese, sell for a lot less and lack the high tech features like the metal neck and EMG pickups.
Wow. Old thread. But I happen to have an XK4 and need to correct some misinfo: The XK was the imported, down priced model, without EMGs (Hartkes instead) but with the same Vaccaro alum neck as the XL.
I picked this bass up 4 or 5 years ago for $150 on the 'bay and never quite found a sound I liked. Fast forward a little and I had left the XK at the rehearsal space for a long term band engagement. During that time, I figured out the sound and got to like the little scamp. My bandmates loved
the sound and would pester me to gig with the XL instead of my Modulus (go figure). Frankly, I would have played it out if it weren't so ugly! The 80s modern body, the cheap aluminum anodized guard... Ugh.
Well the band broke up recently and the first thing I did when I got the bass home was to shorten and reshape the lower horn and reshape the upper horn. I'm waiting for a fresh black nitro finish to dry and get polished out while Pickguardian is making a brown tort guard that fits the new, modernized body shape. So the ugly duckling is gonna do a swan thing and still sound great. Net investment: Less than $300. My Modulus and other thoroughbred basses are pissed off already!