First, I own an Ayre K-1XE, just so you know where I am coming from.
The Ayre K-1XE is a great preamp. It has very good phono boards. They are very musical and have great frequency extension. The imaging and soundstaging is also very good. Its strength is the very deep, dark background it presents. (I hate tube rushing, so this is a blessing). As a line stage it is excellent. It is much better than the ARC LS-2 (preamp) and PH-3 (phono preamp) that it replaced. (It also has a volume/mute remote control if that matters to you. It did to me!)
That being said, if you are planning to buy a seperate phono preamp, the Steelhead would probably be a better choice. I have only heard the Steelhead briefly, so am basing this on my research and the reviews I have read. According to the reviews, and people whose opinions I respect, have said it is one of the best available. But then again, it should be better, since it costs almost as much as the Ayre K-1XE, which is a full function preamp.) I do not believe that the Manley will offer balanced inputs, or outputs.
If you have the cash to afford the Manley, that is probably the way to go. As for using it as a preamp, I would recommend going with a dedicated preamp instead, as it will allow you more flexibility, as there would only be one input in the Manley. (Plus this is the first version of the Steelhead, with the preamp function, and they will probably modify it once they have some more time and experience with the unit. Manley is pretty good about updating their equipment once they figure out how to make it better. Something that Ayre is good at too, by the way!)
If on the other hand, you only have just enough money for one unit, and you have more than one input, I highly recommend the Ayre K-1XE, as a full function preamp. The Ayre K-1XE has 6 inputs (3 balanced, and 3 single ended). (I use five of them myself.)
If I were grading it as Stereophile grades, I would give the Ayre line stage an A-, and the phono stage a B+. Stereophile gives the Steelhead an A.
(By the way, unlike Stereophile, I do not believe in giving out A+ grades. I can not believe that Stereophile does that now!)
Perhaps an Ayre K-1XE, without the phono boards, but with a Manley Steelhead. That might make a great combination.
Good Luck in your search!