I generally use the TV speakers if I want to use speakers at all (using hdmi cable), but I generally stick with the headset, as I'm sure my neighbours wouldn't appreciate blasting metal a whole lot :P (The tv is on the shared wall).
There's some room, (I don't tend to exaggerate my hand movements) but it is a little tight. The K90 has the G buttons on the left side so if they weren't there, it'd be fine
P.s. I'm glad that you guys like it