What source are you using? @invalid is right but, as your amp is fully balanced, to preserve that you’d need a fully balanced pre rather than a pre with balanced connections but is not fully balanced from input to output. By requiring a fully balanced preamp you’ll greatly limit your choices at your price level, which is something to consider as going fully balanced is just one in a loooong list of design features that affect ultimate sound quality so you need to balance those based on what’s most important to you. Dual differential is nice to be sure, but it comes at a price as you’ve already discovered so weigh that against what you’d be giving up (i.e. maybe getting an even higher end single-ended pre rather than a lower-end balanced pre for the same $$$). Always trade offs in this hobby.
IME of the three brands mentioned the VAC will likely provide a little more warmth that you seem to be looking for while the ARC and Atma-Sphere will skew more neutral (although this can be altered by using different tubes) all of them make excellent preamps, and at this level it really comes down to personal tastes and system synergy, which is what can making an ultimate choice difficult. I don’t know if Underwood offers a return policy (maybe with a restocking fee, paying return shipping, etc.) on the Audio GD, but if so and depending on the terms that’d be well worth considering as nothing beats an in-home demo and it seems like a good fit from a respected designer. Hope this helps somewhat.