Ayre V-5xe best tube pre-amp to match with?

I don't have, but have heard Ayre amps paired very nicely with VTL tube preamps. Very musical combo. The VTL 7.5 is amazing, but very pricey; believe the new 6.5 or even the 5.5 might be a match.

Frankpiet, I thought of going with an Ayre pre with my V-5xe, but wanted tubes in the chain. After a ton of research I went with the BAT VK51-SE. If you don't mind the price of the BAT, I think it's as close to a perfect match as you could ask for. The venerable Mr. Bigtee and I both found that certain tube preamps will cause a 'hum' when matched with the Ayre. I would highly recommend BAT or try a home demo if you go with another brand.. or check with Ayre to avoid a compatibility issue. Btw, you might check TAS review of the 51SE. The reviewer gave a slight edge (in his opinion) to the BAT when compared to Ayres K1-xe. ..good luck

Bigtee / Classical1: which tube pre´s caused a hum when connected to the V-5xe ?
I´m not familiar with the BAT hause sound, but I´ve heard the best value pre from BAT is the VK 31 SE - is this a good one? I´ve also heard Aesthetix Calypso, CAT SL-1 and Modwright SWL 9.0 SE would be a good match ?

Whatever choice you make get a truly differential balanced preamp. The Ayre gear is meant to be run with a balanced signal and although it sounds okay single-ended balanced is the way to go. The mere presence of XLR outputs on the preamp does not necessarily imply a balanced signal. Atma-Sphere, Audio Research and BAT are balanced and I believe Aesthetix is too. CAT, ModWright, Herron and (most- perhaps all) VTL are single-ended.
Ultimately there are better preamps than the K-5xe or K-3x but within their price range I haven't heard a preamp that is absolutely better. The affordable tube preamps are more different than better in any absolute sense.

Frankpiet - I had trouble with a DeHavilland Ultra Verve when matching with Ayre. This is in NO way a knock on the DeHavilland as it worked fine with another SS amp, and at it's price I think it's one of the best buys out there.. but for some reason it and the Ayre wern't compatible.(Hum) The deHavilland is single ended.