130 Pro USB skipping?

[DelaneyB]

OK,
I'm helping out a friend with a new/used 130 pro
She connected her new mac book air to it to stream spotify and it 'skips' and crunches...
Its a Pro 130 with HW 6.0 and FW 10.1.0
CD player via line in - no problem

So I'VE brought my 2012 mac book pro along to trouble shoot.
Wi fi is working fine with a good signal and Qobuz in CD quality plays fine on:
- internal speakers
- Optical out into Devialet via Toslink

But USB (via a good quality chord USB cable that is known to work OK) cd quality stutters to a halt.. 320 streaming plays but skips every minute of so..

Any ideas?
She cant use optical out or AIR as she has a 2019 MBA with the latest Mac OS (Catalina).
Tx
Brendan