I cannot say I know the Goldmund Telos 400. But I know the Halcro very well.
Both are very honest amps from what I understand and some of the finest on the planet. Both add nothing to sweeten or color the sound. I have heard it said that the Telos 400 is much more alive than the Halcro.
The halcro is a very pure listen, and some people say it is clinical or cold. I wouldnt say its clinical, it just has no sound if you know what I mean. I suspect while the Ref3 pre will bring noise to an otherwise totally clean Halcro it may well add life to it and will work well.
It may well be worth having a listen to the Luxman B1000f too.
Hope this helps.