Zu Audio Omen MKII

Hi brimel,
I don't own Omens but I own 2 other pair of Zu speakers (Superfly and DefHead).  I can't answer your question directly, but I have upgraded the drivers on my Superflys, so I can offer some perspective.  The new drivers on Omen mkII should sound subtly but noticeably better.  In my own experience, the new drivers were just a touch more effortless, a bit more oomph (or "shove" as Zu likes to say), just a bit more "there".  Again, subtle but noticeable.  

The key word is "subtle", meaning if your budget only allows for a used pair of mkI, don't feel like you are missing out on a world of sound.  Your best bet might be to wait until Zu offers their $999 Dirty Weekend II sale again, those now use the new drivers but without the upgraded capacitors and level of fit/finish in mkII, which you can see in the chart here:

http://www.zuaudio.com/loudspeakers/omen-dirty-weekend-2

My personal take is that you get what you pay for with the mkII upgrade but used mk1 is still a nice entry point.  It's up to you to decide on the tradeoffs.

Zu does shows with Peachtree all the time so your amp should be fine.

Hi jesusaO,
You should check out 213Cobra's post entitled Zu Druid & Definition Roundup.
He addresses the differences between Druids at the beginning of what is a very long post. 
It's very good.
early

early,

I would like to know in which aspects the Druid Vs sound "significantly" better the IVs.

II's are always better than I's. Or at least they should be. I know that my Druid Vs sound significantly better than the IVs. 
Just call Zu. You will get honest info. One of the many things that I like about Zu gear is that it is constantly evolving. When they make improvements to their products, they pass it on to the consumer in a fair manner.
Zu has paired their speakers with Peachtree amps at audio shows if my memory serves me.
Enjoy!