Yoshihiro has released Version two of his Game Decrypter for PSP games that require firmware 5.55 and firmware 6.00 to run. This application allows you to patch the firmware 5.55 and firmware 6.00 eboots in order to run on custom firmware 5.50 GEN-A to B2. It allows you to also run 5.55 and 6.00 FW [...]

Its out!, Download is below. You’ll Also need UMDGEN 4 for this. Decrypts both Firmware 5.55 games and firmware 6.00 games. But not all of them work due to some headers on the prx files.

Edit: Game Decrypter Version 2 is out! Grab it here: Game Decrypter V2
Release text and how to:
..:::Yoshihiro’s 5.55 & 6.00 games [...]

Bosshunter has also released a his own IR Shell 5 patch, similar to joshd666’s iR Shell 3.9 patch for 5.50 GEN-A & GEN-B. Bosshunter’s patch allows 5.50 GEN-A users play ISOS and also improves the stability of IrShell on Custom Firmware 5.50.
Release Notes:

Note 1: PSX games will only work with flash POP Ver (won’t work [...]

Matchung has done some work of his own on unofficial CXMB for custom firmware 5.50 GEN-A, improving it as its reported to work much better now. Not to mention that it now properly lists the themes under the [Settings]. Also included in the archive are ctf.exe and unctf.exe. These are used for decompiling and recompiling [...]

GENyUS has released a popsloader module for his Custom Firmware 5.50 GEN-A, with this plug-in release uses if need be can select which pops version to use for further PSX game compatibility.
How to install the Popsloader 5.50GEN:
* Download Popsloader for 5.50GEN in the link below
* Connect your PSP to your computer via USB
* Downloaded file [...]

PSPGen have released CXMB for Custom Firmware 5.50 GEN-A, while its still in a beta stage it will allow 5.50 GEN-A users to use CXMB CTF themes. Its an unofficial version of Poison’s CXMB. It also loads the CTF themes without touching your PSP Flash memory, which is risky.
Source: PSPGen (French)

GENyUS and PSPGen have released their Custom Firmware 5.50GEN-A for PSP-1000 and PSP-2000 v1 & v2 only. This custom firmware supports official 5.50 features with Popsloader PSX and ISO support. There is also the option to hide your MAC address.
Update: Custom Firmware 5.50GEN-A build 4 has been released to fix the PSN network bug. Please [...]

GENyUS and the guys behind 5.03 GEN-A firmware for the PSP-3000 are working on Custom Firmware 5.50 GEN-A. Custom Firmware 5.50 GEN-A which will be out soon will give users the features of 5.50 but with the homebrew options of GEN Custom Firmware. Reading the translations from French its clear the PSP-1000 and PSP-2000 are [...]