I really love the sound of certain AA6 sets. Not all of them... but some.
Every now and then as I'm rebuilding a set and I get rewarded with one that just has wonderful qualities about the sound and performance in general.
I can't put my finger on it exactly...
Not sure if it's due to the extra RF stage or the size and design of the speaker or what.. I don't know for sure but I DO know they just sound great.
The audio has a nice rich deep base and there is quiet between stations as I tune across the dial.

I don't think ALL AA6 sets are great nor are all AA5s mediocre.
I have a couple AA5s here too that have that "good sound" as well.

The two AA6 sets that I really love both have only a 5 inch speaker too.
They are:
Majestic 6T120
http://www.nostalgiaair.org/PagesByModel/590/M0010590.pdf

Airline 14wg625A
http://www.nostalgiaair.org/PagesByModel/133/M0011133.pdf

I think the two AA5s I really like may have 6" speakers ... but can't remember now... and those are both Emersons.

Emerson EC:
http://www.nostalgiaair.org/PagesByModel/053/M0005053.pdf

Emerson 653B
http://www.nostalgiaair.org/PagesByModel/717/M0004717.pdf

I know what you mean about a good radio with an RF amp. I have a Silvertone 1017 with a good size oval speaker and tone control. The RF section is tuned with a 3 gang capacitor. The performance and tone quality is about as good as it gets. The volume control has a perfect audio taper. You can zero out the volume, of turn it past 3/4 before any disstortion. The radio is well made with a copper clad chassis, closed on all 4 sides. The dial lamp is a 4 watt 120volt type that lights up the pointer needle made of clear plastic with a red glow. The on off switch is also the radio phono switch so the volume control can be left pre-set. Also you can switch to phono just to mute the radio, then back to radio at the same volume.