Matching phono preamp output impedance to preamp input impedance?

I  got started on vinyl a while back (very bad mistake for my bank account)!
So I started with something used just to try out to see if I like it and now I am
in the process of replacing my initial set up with something better. Anyhow, the 
dealer that I orderd my turntable from gave me some suggestions when looking for
phono preamp. Basically since my preamp input impedance is 10k ohm, he suggests
that ideally I should not be looking for any phono preamp that has output impedance above 100 ohms.
This proves to be a big problem for me. This particular dealer carry only  Asthetix and Leben phono
preamp which he said I should not even think about as both  would not match my pre amp due to their
much higher output impedance. So far, Only EAR 324 seems to fit the bill (60 ohm). I can arrange to audition EAR 324 and
few other phono preamps in my system (Graham Slee Gold Reflex, ASR mini) also but there are also many many other good phono
preamps that I want to consider but I will not be able to audition them in my system so I have some concerns even if they
sound good in the store, whether it will work well in my system.
I wonder how importance or significant is this matching input and output impedance of phono pre and preamp
and is there any hard and fast rule about this?
 
Thanks for any advise regarding this matter.