I am also wondering if anyone has had this issue with the 10.33 (WM8741 chip).
One thing that might help is a cheap toslink-coax converter. I run an optical through my TV to my AGD DAC and it would cut out (don't know why). I had a Monoprice converter not being used so I tried that, seems to work now without cutting out.
Also, I have discovered that not all optical cables work as well as others, some seem to hold signal better (for lack of a better term).
I have an older NFB-10 and I get sound regardless of the position of the internal jumpers (fixed or variable) - you should get the same.
If you go with variable (preamp) output the volume control of NFB-10 works and you can adjust the speakers volume at will.
If you have not opened the case how have you observed both output modes ?
If you cannot find any connection mistake, I suppose you can live with that - I always keep the jumpers to variant mode.
I suppose you have tried both rca outputs and both gain settings, as well as a 2nd pair of interconnects. If the xlr output is working on fixed mode, you could check whether the speakers require more than 2,5 V input (unlikely).
Look at some previous reviews, impressions from older models like nfb10wm, nfb2, nfb3, compass 8741 etc, and i am sure you should get plenty of impressions how 10.33 sounds.
Though some of which i list here are only dacs, this is how the sound signature of 10.33 should be like.
Comparable to the nfb28, a signature house sound with a slightly different sound flavour due to the dac used.
I own the NFB10 with the WM8741 chips I'm using the balance out the sound quality is "neutral" but with lots of detail and grat "soundstage" and depth.
When I first used the NFB10I only had single ended headphones SQ was Good however Balance headphones will reward you with best performance.
Yes, the build quality and performance is exceptional I own 4 Audio GD components and I'm very satisfied with the sound quality and performance. The only recommendation if you purchase it is break in for 200 Hours as it will reward you with superb sound.