I wont comment on Rileys ROM in this Forum but I used Rileys ROM when I first bought the M9 Pro 5 years ago and all I can say is Arctablets ROM for M9Pro is stable . I have been using the Tab for 4 years plus now on ArchTablet M9Pro ROM. 

The ROM is Android KK 4.4.2 and your Android JB 4.2.2 we have used that version before and the factory ROM sucks no matter how we modified it remains very unstable. So we pressured the factory to give us the upgrade to 4.4.2 that they promised. Even the factory 4.4.2 was released in 3 version (if I am not wrong) only on the 3rd version do we have a stable version.

You can use the CWM Recovery from Archtablet or TWRP Recovery attached

To unbrick  see this topic : http://www.arctablet.com/blog/forum/pipo-max-m9/pipo-m9-pro-brick-hard-solution/#p48160

How to avoid flashing failure : http://www.arctablet.com/blog/forum/firmware-development/i-am-getting-a-download-failed-everytime-i-flash-firmware-on-rkandroid-tool/

Recovering from hardbrick including drivers : http://www.arctablet.com/blog/forum/pipo-max-m9/need-help-with-bricked-pipo-m9-pro/page-6/#p59374