It's the smps in the 3+ usb for sure that's adding the veil = noise. And yes, you can use 5v with the 3+ usb as I have found out.
I also just added another 3+ usb to the chain and modded it with lps.
If I can go to the next upcoming meet, (not sure yet if I could) then you can listen to the rig and see if you hear any diffrence.
I'm also not sure if I'll make the bottlehead meet, or not.
And today I yanked the SMPS out of my 3+usb and powered it up (6.255Vdc) with my dual LPS.
It failed to latch on the aes data stream, and would loose its lock on a SPDIF feed from my 3+ as well.
So I'm investigating getting it repaired, which means sending it back to Germany.
I bought it used so there is no warranty.
But before I send it in I'll try lowering the voltage down from 6.2 to 5.2Vdc to see if that fixes its problem.
I sure hope so because it's not gunna be cheap to get it fixed, what with shipping, let alone the actual repair costs.
One of the prerequisites of DIY is to take responsibility when things go sideways.
And I'm thankfull this sort of thing is rare.