6 ohms is fine, as speaker impedance dips go... and the dynamic impedance of any speaker is naturally all over the place.
The spec sheet in pdf says it all.
the transformer is a 1700va rated unit.
the maximum power draw is 1820va when in stereo mode, with 600 watts per channel continuous at 4 ohms. that’s the max power of the unit, that’s the rating of the transformer. The 1700v rating is an average long term thermal rating, as it is for all AC power transformers.
Dynamically, all transformers can handle higher intermittent short term dynamic loading, as in with bass transients. It’s just that the long term continuous loading is the ’toaster’ load rating. Ie, where the heat will go up to unsustainable levels.
The unit draws less power at 1000 watts mono at 8 ohms. 1330va....but the power draw will rapidly increase as you demand more power at lower impedance at 6 ohms.
The reality is that we rarely draw any real power continuously but mostly hit high power draw in peaks...
It should physically work, but how well, sound quality wise... is up to your testing/listening and how you feel about it.
It appears to be as if you would be stacking or bridging a pair of already bridged amps? Each channel is already a bridged design?
They are not giving you the slew rate, as that would generally be a dead give away if it is a balanced bridged design or not. Nor does my quick scan mention any thing about whether the grounds or negative terminal for the speakers is sensitive to being cross connected.
450 watts per channel into 8 ohms, tends to be saying it is a balanced/bridged design for each channel already, so I think you would be stacking balanced/bridge channels. Probably should not be run below 8 ohms (nominal) as speaker loads go.
You really need to look at your speaker’s impedance curves carefully. If the dip truly does not go below 6 ohms, then it might be fine.
Essentially, there is no assurance of anything for anything.
https://revelspeakers.com/productdetail/~/product/salon2.html
If this is your speaker, the impedance specs say it’s probably not a good idea.
Fine in stereo mode, though.