Far be it for me to bully anyone for their tastes, but even if this album isn't your cup of tea musically, I find it hard to see a world where this is anything less than a 7.
There's plenty of discrete rear channel activity, and even panning effects, like the sound of a flare moving from right to left behind the lyric "some loser fires off a flare, amen..." in Snowbound.
I don't think this album could sound more like it was recorded in 1992 if it tried, and I get if that's not your cup of tea - the sterile sound of the album took a long time to grow on me, but there are some absolute classic Fagen tracks on this album, starting with Snowbound and Tomorrow's Girls.
Like my Fitness Consigliere
@fredblue (who probably owns the worlds largest collection of terrible surround music) said to me in a private conversation recently about another good 5.1 mix that was getting panned, if you think this is a 6, you probably haven't heard many (or any) of the literally hundreds of forgettable 5.1 mixes released by the major labels in the original SACD/DVD-A era circa 2000-2004, which I think are truly emblematic of the kind of mediocrity that a "6" represents.