Do you really hit more than 6 keys at a time when gaming? Spec sheet for the board you mention indicates "full key rollover" so not sure where the 6 is coming from.
Come to think of it, you've got five fingers on one hand. If the other controls a mouse, it's a bit hard to imagine having to hit six keys at once.
Sound is going to come 90% from the switches. Casing isn't going to have much of an effect.
There are probably dozens of linear boards in 60-65. If the Leopold has the switches you want, they have great build quality.
Hey, maybe he's polydactyl, and can reliably hit 7 keys at once, and is playing some kind of insane game where he must type Shift, C, Up, T, End, F5, AND mash Context Menu all at once!
No but seriously, 6 key rollover is for virtually all intents and purposes, unlimited.