AFAIK and have done, you can put EHDs on any of the 3 USB ports. For that matter you can add a 4-way USB hub, powered or not, and use more ports on each of those. I recommend only powering one of the drives into the hub at a time. Limit the total number powered to 3. The port names are assigned in the order recognized, usually, filling from #1. Check the disk size and sample the listing and watch for disk activity.
The 3rd device can be accessed for transfers from Menu button, then 2 down and left wraparound aka the External Hard Drive.
Only the first 2 drives can be accessed for reading/listing/deleting from the DVD button then My Recordings and right to the uncolored button and its drop-down menu.
You could have 3 drives working but doing only one drive at a time is a lot less confusing. LOL
-Ken