So I ordered a 512GB sd card from Amazon - it looked like a Sandisk (the chip colors) - it turns out it wasn't and took a long time to arrive, but I was in no rush. I assume the delay was because they were out, because they sent me a 1TB sd card instead (with no brand name) and the card I ordered is no longer available on Amazon.
It came formatted FAT32 so I followed the instructions for setting it up... it seemed to go through all the motions including setting up the P3. I didn't copy any songs over. It fired up and went into the BB1 opening display, so I shut it down and put in a thumb drive to load a few tunes. When I went to fire it up again, it brought up the BRENNAN logo display and then nothing happened. So I turned power off - it wouldn't turn off - so I held the power button down till it shut down. Tried again a couple of times with the same results. So I pulled the sd card and tried it all again. This time I tried reformatting the card - lo luck - everything I tried refused to format FAT32. BUT - I did find that the Format USB A in the Advanced menu on the BB1 would successfully format the 1TB card to FAT32.
So I ordered a new 512GB card and this time made sure it was a Sandisk card. While I was waiting for it to arrive, I found I already had a 512GB Samsung MicroSDXC EVO Select memory card (not FAT32) and formatted it using the BB1 Advanced menu, followed the rest of the upgrade instructions including copying the P3 from the original card. SUCCESS - all the songs I had installed on the BB1 were there - everything worked and it now reported having 512GB available.
So, I can confirm the the BB1 will work with a 512GB memory card.
I have tried the 1TB card a few time more, but with varying results - the last time I went through all the steps including copying the P3 songs. It seemed to work properly this last time, but seemed very slow doing anything including going to the NEXT song. But when I hooked the BB1 to my Ethernet, it locked up and then wouldn't work again after that, so I put my 512GB card back in and all is working properly.
So my question is... has anyone successfully installed 1 1TB card? I suspect that the problems I had were because of the off-brand 1TB card and not because the BB1 cannot handle a 1TB card.