Lets take a trip back down memory lane, to the time when Blackmagic did the drivers for the original Kona cards. This is a list of previous features from the read me in the 4.0 software release. Note the bold text below.
If you use the Kona Control Panel, and set the output to Macintosh Desktop. You can use your Kona to view Photoshop files on your video monitor. I am not of any other functionality between the two.
The IoLD does what the Kona 2 does (SDI in and out), minus the HD that the Kona adds. It sounds like you have everything you need for now, unless you need Analog HD. If not I would just buy the Kona LHe when you get the Mac Pro.
You should be able to capture directly into FCP with the timecode intact. You might need a capture card or something like an Io to do this though. Just used the RS 422 port for control and bring the audio in directly. It will capture with TC.
I am not 100% sure, but I am 99.999% sure that you cannot have to cards in one machine.
Since the Kona 3 does everything that the LHe does (an more), but analog in, I would think that it would be smarter to save several hundred dollars and buy one of the mini converters (like the HD10AVA) instead.
FCP does not allow you to play back mixed resolution files in one timeline (without rendering). What the Kona will do is play a DVCPRO HD sequence and the outgoing singal from the Kona is uncompressed HD.
You can work with DVCPRO HD on a firewire 400 drive with or without the Kona. The stuff isn’t even 15MB/s. I am getting 100MB/s sustained on my MacBook Pro with 2 SATA drives striped. So you can actually do a whole lot with internal SATA.