Leben Cs600 and LM 219iA

Those are really different  amps.  I think the LM will play with more authority .

As a Leben and LM dealer, there will be a pretty decent difference in sound profiles b/t the two.  Both are excellent integrateds.  LM will give you a lot of that SET midrange/top end "magic".  CS600 is a fantastic integrated though.....

Are you looking for something different soundwise out of what you currently have?  Or just looking for a change?

Gold print, 
As a dealer,  can you elaborate  on the differences more? Also,  where is your store? 
Thanks,  John 

hi5.
Your Leben amplifier has an excellent reputation and I imagine that it's a very good match with the Zu speakers. These 2 amplifiers are fundamentally different designs . Push pull 6l6GC/el 34 compared to 845  (with 300b driver) SET,yep,they're different. Individual taste rules so hard to predict which one you'd choose. Given your music genre preferences the 845 SET would be a superb option.  My bias is in the direction of the LM 219ia. 
Charles 

As Charles mentions above, these are two completely different designs.  Probably as much different in overall sound as there are similarities. 

I've never heard either with the Zu's, so really hard to say which the OP would prefer with his musical tastes.  Both would likely be extremely good however.

For ROXY54 -- I'm located in NC. (Lexington area)

Goldprintaudio, 
The reason I asked where your store is located is because  I live in AZ and Arizona hi from is also a dealer for Leben and Line Magnetic,  and I was wondering if you worked there. 

Thanks Roxy.  I don't work for them, but know them there very well.  Nice group of guys.