I have only had my 60's for about 2 weeks. I have listened both with and without the sub. Mostly without. I think the 60's sound just fine without it, but on the other hand if I had a sub hooked into the system I would probably leave it on. It can't hurt it can only help. When I had the 60's in the HT system I had it set to large and crossed over at 40.
oz

"Life is what happens while your busy making other plans" John Lennon