Hi everyone, Thanks for all the advice on upgrading to the latest firmware on the Kiwisix. 

It all went smoothly, so I thought I would post some tips, plus help for Mac users. 

If using a Mac, SysEx Librarian works great. But as PRAGMATRAX suggested for Windows MidiOX, just make sure the buffer size here is set to 32 in the preferences, the speed works fine at 100%. Having this higher seems to be what has mangled other boards! 

It is probably best to conduct a dry run first and check all works fine. Simple way to do this is get the free Midi Monitor app and plug your midi out cable into your midi in. Then send the Sysex file from SysEx Librarian and check that the resulting input on midi monitor corresponds. If the file size matches exactly you should be all good. In all the 4.0 update took around 40seconds to load this way and the same on actual run to Kiwisix.

Don't play clock or Midi in whilst turning Polysix on - Whilst there is now protection from corrupting your Kiwisix (like V3 did), for me it stops it from turning on now, and just hangs on the start up showing you the firmware version. This gave me a fright, but once sequencer was stopped it booted up.

ARP external sync issues. For me the arp sync to external clock, caused all sorts of crazy results, switching playing modes automatically rendering it useless - so for me I've just got this turned off and arp and sequencer work great. 

ARP - the speed settings are now stored per patch and all start very slow, almost like they are not working. so you will have to go into each patch and edit the global variable arp divider to what works, I just like mine on max.

Hope this helps some people out.