I'm not quite clear what you want, Evolvist.
Could you write a specification?
Do you for example want to keep the windows clear when listening? Or, do you want something in front of it when listening that can be easily moved and stored when not required - more easily moved and stored then a panel on feet, such as a curtain, blinds, or something on rails?
And then, what sound problems are you trying to deal with? A frequency range, say.
For me I see nothing wrong with moving panels on feet. They are not heavy, but perhaps they could be put on castors or rollers. Of course there needs to be a place to store them when not in use, but that applies to any product.