Hi,
As per my original response, Powerlink only BL5s sound rubbish compared to feeding them with Coax. Night and Day in my opinion.
I assume you are feeding your BSCore with 96kHz feed and it is not responding but responding at 48kHz?
The BL5s should be good for 96kHz/24bit DSP so either you have a problem with the Core or the BL5. Again, as indicated above, play with the cables (which is fed first), L/R channel (on Powerlink) and coax1/2 input order. i.e. if 1 BL5 has a DSP problem at 96kHz but ok at 48kHz, you can test each separately. If you have this sample rate problem in both, you have a Core problem (or the signal going in the core is above 96/24). You want the Core to have a problem if you must have a problem.
As I see it now…with the info presented, it sounds like the problem is the Core of the feed to the Core.
Can you connect the Coax directly to your non-Core source but keep the Powerlink in the core. (This will give you Beo volume control but no source control). However, it will help diagnose where your problem is.