The Butler 2250 is rated at 250/250 watts output into 8 ohms, but the input sensitiviy on Butler's web site also is listed at 2V in yielding only 150 watts/channel out into 8 ohms. This is a relatively low voltage gain power amp and will require more gain than most linestages today have, to drive it to full power. This may be why some people find the sound of a Modwright pre "too polite" with the Butler amp. It looks like it requires well over 3V in to be driven to full power out.
So you need a preamp with a lot of gain. The Audiopax Model 5 has 12db and 23db gain options. The outstanding Melody 1688 preamp has 26db of gain. If you can find a Cary SLP50B, it is rated at 20db gain. The Modwright 9.0 maxes at 15 db gain and may not be enough to drive the Butler, depending on the output of your sources. You will certainly NOT be happy with a Placette passive or a TVC like Sonic Euphoria, unless your source has lots of drive and voltage.
BTW, I face the same issue with my Audiopax 88 power amps, which have only 18db of voltage gain. It's not a quality issue. But some of these innovative new architecture tube amps have very modest gain in the input sections. Of the preamps you mentioned, the Blueberry Extreme, at 20db gain, looks like a good place to start.