S8 Autoset spirit & S8 Autoset spirit II

[bouncer]

I know this is a long shot, but does anyone know the difference these two older machines have in the way they provide therapy.
I successfully use the 2008 S8 Autoset Spirit II (95th = always 8 ish/AHI = 1.0 ish or below) - no problems and feel good the next day.
Now bought the 2006 S8 Autoset Spirit (Australian model) as a backup - but pressure only gets up to around 6.4 with AHI over 2 ish ... not bad AHI I know but I feel shattered the next day. I cannot understand why there is a difference; the Spirit II has never given such a low pressure. Has anyone got any ideas??