As a cat owner, I sympathize. When I first looked at those, as well as the SVS PC series Subs, I saw destruction and decimation in my future, as well as the most expensive scratching posts ever! I even went as far as considering building my own perforated metal speaker grills for a speaker I ended up choosing not to buy. Ordinarily, my cats aren't destructive, but its a concern as all cats do this naturally.
Put a good scratching post near the speakers if the cat(s) will be near them unattended. That should be much more attractive to them then the speakers themselves... especially without the cloth cover.
And if you really love the DefTechs... consider this the opportunity to really pimp them out!
You could make your own speaker wrap from any choice of fabric... you could install your own speaker grills even... an unfortunate but potentially fun and rewarding DIY opportunity to make them your own!