New amp recommendations

I agree that matching a REF3 with an Onkyo amplifier is a bit of a mis-match... but who cares. This is a hobby and if you want to give it a try, go for it.

I think it makes more sense to buy a component that you really want (like a REF3) and plan to keep, than buy two components which you know you will flip down the road and possibly lose money on.

What about the smaller ar ls26?

Keep the Onkyo, you are not going to gain much if anything replacing it with another amp from an audible standpoint unless your just looking for more power. http://www.tom-morrow-land.com/tests/ampchall/index.htm

I'll keep the Onkyo amo. Still undecided between ARS LS26 and Ref.3 preamp (both of which I will try to audition). Is the Ref.3 worth 2k euros more than the ls26 (used)?

For the same money - less actually you could get a Audio Research VSi60 Integrated. Very nice sounding amplifier.