QoS Prioritization for VoIP using DiffServ

Hello,

I am trying to understand and configure QoS prioritization for VoIP using DiffServ (46).  

I find this configuration very counter-intuitive, but we have about 50 of them, so I have to figure this out.

1st question - is it enough to simply go into DSCP to queue mapping and change the EF (DSCP 46) to queue 3?  Does this mean that all traffic marked with the DSCP 46 EF header will be in the highest queue and therefore takthe mose t priority? Incidentally, I don't understand why any DSCP attributes are configured under CoS as CoS is technically for L2 and DiffServ (DSCP) is strictly L3 (this is one area that is very counter-intuitive to me), but as long as I understand HOW to do it, I guess this doesn't matter.

2nd question - If my above statement regarding the DSCP to queue mapping is correct (all you have to do is change EF (DSCP 46) to queue 3), why would anyone create a policy configuraton, mapping a policy attribute (queue 3) to a class (Service Type = DSCP ef) as described in the following Netgear KB: "https://kb.netgear.com/21757/How-do-I-configure-differentiated-services-DiffServ-for-Voice-over-IP-VoIP-using-the-web-interface-on-my-managed-switch"?

Much of this KB doesn't make sense either becasue you can't assign a queue AND mark a DSCP value as it says, but I'm assuming this is due to the model and firmware differences, etc... Unfortunately, I find there are errors in most of the KB articles I've found thus far, and it is difficult to find the exact information I'm looking for (for this particular switch).  Hoperfully someone can help me out here...

Thank you!