The JPX 825 is slightly larger, has a thicker topline (when you look down at the iron from above it doesn't look too 'blade' like) and a little more offset I believe (easier to square the ball at impact). The lofts are also stronger by 1 degree.
To be honest, you need to trust the fitter, more often than not it's all about the shaft of the iron, I use tour stiff shafts in my woods, regular in my irons and stiff in my wedges, a right mismatch but it works for me.
The lie angle of a club is about how it sits level to the floor at address, so if the heel or toe of the club is up then you will need the lie altering either upright or flat to compensate (I'm a short arse and my swing means I have 2 degree flat lie). Loft is about launch angle from the club face, but bear in mind that can also be altered by your swing, shaft etc.
To be honest, you need to trust the fitter, more often than not it's all about the shaft of the iron, I use tour stiff shafts in my woods, regular in my irons and stiff in my wedges, a right mismatch but it works for me.
The lie angle of a club is about how it sits level to the floor at address, so if the heel or toe of the club is up then you will need the lie altering either upright or flat to compensate (I'm a short arse and my swing means I have 2 degree flat lie). Loft is about launch angle from the club face, but bear in mind that can also be altered by your swing, shaft etc.