AJA currently has three main HD I/O cards for use in a PC, the Xena HS, the Xena LHe and the Xena 2Ke. The LH and 2K come in PCIe and PCI-X varients, which are otherwise identical to my knowledge. All of these AJA cards support 10bit color and 23.976/24p frame rates. (The Xena HD was AJA’s first HD card for PC, and was identical to the HS except that the HS now includes Standard Def SDI support)
The Xena HS is a simple card that only supports single channel HD-SDI (422) and 6 channels of AES audio. The lack of analog audio options can be a significant hinderance. Their are sync issue when trying to use the sound card audio and the Xena SDI for picture. It does allow realtime preview of surround sound which the newer LHe does not. I recommend get speakers that allow direct connection of AES audio. I have used ones from Roland and JBL that work well. Using AES convertors to get analog signal can be a real pain.
The Xena LHe has many more features, most importantly analog audio and video support. Component HD video I/O, as well as stereo XLR I/O. My favorite feature of this card, as well as the HS is that they support realtime capture and encoding of Cineform AVI files, and realtime playback and effects from CineformRT in Adobe Premiere. The big missing feature missing from the LHe is surround sound support. I have not found a way to monitor surround in realtime with the LHe without having sync problems. Keep in mind, this is only with the Cineform RT engine. I have never tried with native AJA uncompressed files.
The Xena 2Ke is a card I have not used, but this is what I know. It is similar to the LHe and adds support for 8 channel audio I/O, dual link SDI for 444 RGB, and HSDL (High Speed Data Link) mode for 2K. Xena handles 2048x1080p24 in realtime, and 2048×1556 at 15fps. (not realtime) In the Apple world, the same basic card is called the Kona3. The only feature missing that is found on the LHe is analog component HD input. It does have analog HD output though.
There are a few disadvantages I am aware of compared to the competition. No conversion capability like a Multibridge, few realtime effects like an AXIO, and no single card has all the I/O you might want. They have no support for DVI or HDMI out for more economical monitoring solutions. Their implementation of 2K over HSDL is not as simple or fast as 3Gb/s SDI, but the card was developed before that standard was created.