Subwoofers with current source First Watt?

All, I’ve got a rather esoteric question that I hope those of you more technically minded than me might be able to help answer.

Today, I tried hooking up a pair of REL subs in stereo configuration to my First Watt F2-J via the high level Speakon connection. I won’t bore you with all the details of my daylong adventure, but both the subs and the amp behaved strangely connected this way; the sub seemed to significantly reduce the amp’s volume in one channel, while the subs themselves appeared to be receiving very little signal. This was consistent even when swapping the subs to different channels, changing the cords out, etc. Strangely, plugging in and unplugging the sub would change the amp’s volume, even if the sub was turned off. Unsettling stuff.

The F2-J is a current source amp - would that explain these strange results? Is it just not possible to run subs from this amp? Is there any danger to amp or subs here?

I also tried the subs with my SIT-3, which seemed to work appropriately. (Results were still unsatisfying, on the whole, but that’s an entirely different topic.)
I know there are some issues with running subs from Pass Labs amps, so I just want to make sure I’m not trying anything stupid with my First Watts. I can email Nelson about this as well but thought others here might have some thoughts to offer.

Thanks!