They're out of my price range so I haven't done a ton of research on them, but if someone put a gun to my head and told me to buy a spendy DAC I'd probably get a Benckmark DAC1. The Anedio D1 also measures very well, but you'll probably want balanced output for your amps and the D1 only has RCA outputs.
I only really know about those because they're up near the top of the line as far as measurements go, so I've got no idea about anything near the price of your current DAC, though I've seen used DAC1s on ebay go for around that price here in the States.
There are probably all sorts of cheaper outboard DACs that might be indistinguishable from those even under the high sensitivity of an ABX test but with something like the Benchmark at least you know where your money's gone, even if its to improvements that are beyond human hearing.
I'd like to throw my hat in and say, if the DAC1 is too spendy and you don't need USB the DacMagic is also very good. It measured in-line with the Benchmark when USB was not used at Stereophile (USB experienced substantially more jitter due too noisy PC PSU's, laptops on battery fared much better though).