Since then, I have happily been using my DX90 with Napcha's dual boot loader - the 9 June 2015 current version of Rockbox and Mango (pretty sure it was version 2.3.0 + L1 dated 1 July 2015). I have got used to Rockbox and have sometimes use it and sometimes Mango. I have read through many of the recent posts in this thread in the past few months but am unclear what the main benefits are for the newer versions, particularly v2.4.0 and v2.5.1. Is it worth me upgrading my dual boot loader to the January 2016 "Cholero" versions 2.4.0 currently showing on napcha's site (Mango only or dual boot loader?) or is the version v2.5.1 L3 that was mentioned in post number 1261 (Yong Xu) the best version to upgrade to? Also I cannot see v2.5.1 L3 on napcha's site yet.
And if I do upgrade to one of the newer modded versions above, I assume that I do not also have to reinstall Rockbox (which is currently on the dx90 internal drive), as that version back in June 2015 does not seem to have been updated. If I am correct, then based on the instructions on napcha's website, it seems that all I have to do is leave the rockbox folder as it is (already installed) on the internal storage, and separately upgrade Mango by downloading the update.img from the newer version 2.4.0 or 2.5.1 of the dual loader, and install it using the "overwrite" option.