NAD C-388 w/BluOS2i WiFi Connectivity

I have a NAD C-388 w/BluOS2i (and HDM-2) MDC cards. It has worked very well for several years.
Later, I purchased a Node2i. They are both in my 2-ch music listening/concert watching system. Typically use PC, tablet, or Note phone to control the C-388 using BluOS app to stream AmazonPrimeMusicHD.

Between C-388 and Node2i, I prefer to use the C-388 because it is more direct connection, since the Node2i is connected to Coax1 input of the C-388. However, the C-388 seems to drop the WiFi connection after 5-10 minutes of play. My solution has been to switch to the Node2i - which has always been rock-solid connection.

Investigating this issue, I've found that the Node2i is always connected on 5GHz (never fails), while the C-388 is always connected on 2.5GHz. Home network is all Asus mesh, with AC3100 (master) and three AC1900 (nodes) spread throughout the house and to cover an acre of property (for IEM noise-blocking + tunes while mowing).

Question is about the C-388 WiFi being 'stuck' in 2.5GHz. Seems I need to move it to the more robust 5GHz.

Anyone know if this is possible and how to do that? Is it a C-388 setting or BluOS2i setting?