JasonNYC - Thank you for passing my request to be able to install xapx files to the developer team. I just successfully installed the new firmware 1.52 and also successfully installed (and all are working) new versions of the Open Service applications: Amazon Music 16.9.7; Apple Music 3.2.1; Pandora Music 2003.2; Qobuz 5.6.3; SiriusXM 5.5.12; SoundCloud 2020.04.06; Tidal 2.23.0; and TuneIn Radio 24.0.1. For those of you that would like to use streaming apps with this firmware 1.52, you would copy any apk files into the device's Internal OpenService folder, and install from the Services selection on the device's menu, but for any of the xapk files, you would first need to copy over XAPK Installer - Rush Wars Installer 2.2.2, and then open that app to use its' interface to install any of the xapk files that you also copy over to the OpenService folder on your device.
OK, so I had only one issue which I need JasonNYC's assistance with - The current Spotify 8.5.51.941 xapk is a "bundle" that downloads from the apktada.com web site. It is downloaded as a .zip file extension and when unzipped is 4 files plus instructions (see attached). The How-to-install.txt file specifies that you have "split" apk files that require the use of the "Split APKs Installer" which I gather is used to put it back into one xapk (or will it be a large apk) file. Unfortunately, the "Split APKs Installer" is not supported on the device, so how do I install this newer version of Spotify? FYI, I am successfully using an older apk version of Spotify 8.5.24.762.
By the way, this is my third A&K DAP and I have never noticed any sound quality differences with firmware and/or app updates.
Thank you for your assistance and stay safe.