Gav
Two other brands that offer excellent preamps are Aries Cerat and Phasemation. I believe they are both available with balances outputs. I've heard our speakers in many system with all kinds of equipment and one of the best (definitely in the top 3) systems was all Phasemation electronics. I haven't heard a full Aries Cerat system but their components are quite good.
I find it interesting that you included the Trinnov Amethyst. The Amethyst is more of a one box solution for people who are looking for a DSP/Room Correction processor with a few preamp control functions. While it's a decent performer as a preamp it's not in the same league. In full disclosure, we sell Trinnov DSP/Room Correction processors with our speakers. For our most discerning customers we suggest using a ST2 HiFi in between their preamp and amplifiers.
You might consider keeping your Wavac preamps and using a Trinnov ST2 HiFi between the preamp and amp. This arrangement will give you an additional pair of balanced XLR outputs for your subwoofers and excellent bass management tools. Send a PM if you want more info and examples of this setup.
Mike