The 1400 initially shipped with 7.5.3 + an enabler, up until the 1400c/166 (and possibly the 1400c/133). I got a brand new 1400 back in the day and it came with 7.6.1 preinstalled. The installation CD also came with 7.6 and the 7.6.1 updater. The 1400c/166 definitely will not boot 7.5.3, and from memory I don't think mine will boot 7.5.5 either.

Regarding the Kanga, it actually will run 7.6.1 I believe. The TAM also originally shipped with 7.6.1, and I doubt it will run anything less. The 3400 is based on a whole new architecture, that one definitely needs 7.6.