I agree with the above poster who said its a probably a toss up between the models you are considering.
If I may make a suggestion. Consider, for not too much more, the Marantz PM8004. In fact, some smart shopping may get you one at or less than the the list price of a PM6004. Now here is an amp that is definitely a cut above all the ones you are considering.
It is built in Marantz' reference factory in Japan and is not afraid to posts its true specs - 70 wpc into 8 Ohms, 100 wpc into 4, > 100 damping factor and 25 amps of peak current capacity. These are specs that will rival integrateds costing a whole lot more. I heard this amp driving a pair of Sonus Faber Cremona M's, a 4 Ohm 10K pair of speakers and the sound was truly impressive. Good luck.