The Antek AN-8425 has four windings of 25 V. The AN-8225 has two windings of 25 V. They're both 800 VA transformers. Either can be used with the Power-686 (and Modulus-686).
If you're using a single Power-686 the AN-8225 would be easier to work with. With the AN-8425 and a single Power-686, you would have to wrestle two wires into each terminal of the Power-686 input. Depending on which wire gauge Antek is using that could require that you solder the wires together to a single wire and then connect this single wire to the Power-686 input. I would think that there's enough room for both wires in one terminal, though.
On the other hand, if you're going for a dual-mono build and use two Power-686 boards, the AN-8425 is actually preferred. You simply connect two of the 25 V windings to one Power-686 and the other two to the second Power-686.
Some may argue that using a single transformer in a dual-mono build is not True Dual-Mono™. There's some validity to that argument, but any difference between a two-transformer dual-mono and a single-transformer, four-winding, dual-mono will be at the dBGF level. That's dB referenced to one imperial gnat fart.
Four windings on one core will couple more than four windings on two cores, but the two cores still couple though their primaries. The Modulus-686 is not very sensitive to the power supply, so I always encourage folks to build with a single four-winding transformer if one is available. It makes the chassis design and layout much friendlier.
Regardless of which configuration you use, do make sure that you get the phases connected correctly to the Power-686. I write about that in the Power-686 design doc. Also note that Antek tins the wire ends. I recommend that you cut that off and strip the wire so you have un-tinned stranded wires into the terminal blocks. Solder compresses in the terminals and over time the connections will become loose if you use the tinned ends.
Tom