I have both the 5900/A11 and the 3910 at the moment.
Even though the 5900 is a lot better in it's build quality (it weights a ton

) so presumably has a better power supply etc. . . .
I was hard pressed to spot any huge difference in audio quality. The 5900 was a tad better it seemed, in stereo with analog connections, a cleaner sound. But other than that it, was much of a muchness.
But even if the 5900 does have more of an advantage in audio than the 3910, as many people would argue, I'd still go for the 3910 as it has the better video side, and all the, or I should say, most of the bugs have been ironed out overall.
The 3910 is the replacement for the 5900, so theoretically, everything, sound quality, components used, should be just as good, or better (bar build quality) than the 5900.
And this is looking in hindsight, as I asked a similar question a month or so ago, about which to get. But now that I have both for testing, the 3910 comes out on top. You can read here, it may help a bit
Click Me and also, have a look over at AVSforum, there is a lot of detailed discussion on the 3910 and the 5900 and how they perform, if you are interested.
Also, the 3910 is a bit more future proof with HDMI. Though then I suppose you could wait for HD DVD players.
I use the iLink connection anyway now to a Z9, so the audio part of the player does not worry me much. But in your case, either one will be a large upgrade over the 2900.
Good pickings
cheers
KJ