Thanks for replying again and for your detailed help. I figured that if it didn't work I could always return it so I picked up a Harmony 900 and did a little testing. (Unfortunately the extra blasters, cables, etc. weren't available.)
I wasn't able to find clear answers online ahead of time, but after looking in the box I realize I made a few mistakes. I thought the precision cables plugged into the mini-blasters, but instead they plug into the (main) blaster IN PLACE OF the mini-blasters. Also, as you mention the main blaster only has two ports. Hopefully that didn't confuse anyone too much. (I really with Logitech's pages gave more details...)
With just what comes in the Harmony 900 box, it looks like these are the ways to control each device.
1) IR from remote (that's what configuration 1 was supposed to show)
2) RF from remote to blaster, mini-blaster plugged into Port A of blaster, IR from mini-blaster to device
3) Same as 2 except for use Port B
4) RF from remote to blaster, IR from blaster to device
Of course as you mentioned for all of these care must be taken so that the IR signals only reach the desired devices. This can be mitigated by using precision cables, so that 2 (and 3) change to:
2*) RF from remote to blaster, flasher cable plugged into Port A of blaster going to device (via precision IR)
If adding blasters allows devices to be assigned to specific ports on specific blasters (I'm still not sure if that is true), then each blaster added would conceivably let you control two more identical devices.
I think with all of that I have enough information to know that this will work for me. Thanks again for taking the time to spell that all out for me. Hopefully this can help others with similar questions too :-)
Originally Posted by dalto
One last minor note note I would make is that they are not IR receivers, they are RF receivers and logitech calls them blasters.
Whoops! I guess when I spend too long searching for solutions online they all start to run together and I forget which one is RF and which one is IR. I made the same mistake in a couple places in that first post -- sorry for the confusion. Thanks for the correction :-)
I've reread this post a bunch of times so hopefully I didn't make the same mistake again...
EDIT: I mistakenly had 4 out of the box methods when there are only three. I think it is correct now.