Sorry, should have edited this before now. I found out that upon trying to recreate using EQ on USB DAC mode with the BTR5 it turns out that it must have been 1 of 2 things, both of which involve a BT connection vs the USB DAC connection.
1) When switching from BT to USB DAC mode the BTR5 didn't actually do that completely - I must have still been on BT.
2) When firmly connected via USB DAC I must have pushed up the BTR5 in it's leather case and the cable slightly dislodged and the BTR5 switched to BT.
The odd thing is I used the BTR5 EQ back and forth for a long time and checked the display every time to see if I was still seeing the 384k instead of APTX, so I don't know how the BTR5 could have been in BT mode - it's very strange.
I'm adding this as I was looking for this post to add what I just experienced with the BTR3k I just got today. It seems to be connected to both BT and USB DAC at the same time, as I even thought the USB cable was firmly in place it didn't sound like it switched out of BT and in to USB DAC mode - so I had to disable BT on the PC and then the audio changed right as I disabled BT.
I'm gonna need to see what's really going on at that transition point between switching from BT to USB DAC mode when connecting / disconnecting the USB cable from the BTR5 and BTR3K.
I'll post a reply when I get those results, eventually...
@FiiO - I've noticed that the BTR5 EQ actually "works" over USB DAC.
After switching over from IEM's on 2.5mm to over the ear headphones 3.5mm - driving them at H Gain and higher volume (100% on PC) set to mid 20's on the BTR5, I finally can hear real effects from the EQ settings.
On my IEM's the EQ doesn't kick in at all, maybe the Gain / Volume are not high enough?
The BTR5 doesn't act like a "loudness" EQ that affects low volume playback, so far as I've experienced the BTR5 EQ it needs serious drive to have a discernable effect.
I've found movie soundtracks using EQ "Classic" are more dynamic, with EQ Hip Hop a bit less so, and EQ Jazz (clear voicing) is good for clarity. I haven't tried any custom / User settings yet.
I also played a bit with the Filters. I wouldn't swear it's so, but I think I enjoy Fast over Slow, and both those over the default APOD 1.