Strangely the tech specs for that Pro-Ject box list its BT codecs as ‘aptX, aptX Adaptive, aptX HD’ without including SBC. Roam only understands SBC and AAC.

If the box really doesn’t do SBC that would explain things, but I’d be amazed if that were the case. I thought SBC was supposed to be a mandatory fallback. 

(In contrast, the BT Box E HD explicitly says ‘aptX, aptX HD, SBC’.)

I agree it’s confusing. It’s even more confusing that the box E HD is meant to be paired so I’d have expected the E BT to have SBC at a minimum. I might need to contact Pro-Ject but I would have thought it would have been supported. It lists its Bluetooth as 5.2 but doesn’t expand any further outwith the AptX support. 

I suppose it’s conceivable that the Phono Box E BT 5 disabled SBC on the grounds that, well, SBC is rather an inferior codec (to put it politely) compared to the fidelity of the others.

The BT Box E HD, on the other hand, as a more general-purpose device would need to cater for all comers. 

Obviously a Phono Box E BT 5 and a BT Box E HD would be expected to negotiate aptX-HD between them if paired together.

See what Pro-Ject have to say.

The distributer has confirmed to me that they’ve reached out to Pro-Ject for an answer.

Will post back with their findings as might help others.