Depending upon what kind of music you listen to, using Q300's without a sub can be OK though even with good stands or solid flat surface there's certain types of music with more bass than Q300's could ever deliver.
Your satisfaction without your sub running is an indicator to me that you don't listen to that type of music and/or your subwoofer isn't a particularly high-achiever.
Hi KenM10759, thanks for your response - nice to know someone reads this stuff and is prepared to respond.
You are likely right about "type of music" and you may be right that the Denon based subwoofer bought from a local Hi Fi dealer (150W, 12 inch driver, 5 db boost at the low end, 25Hz) may not be a good achiever.
I have used it extensively for HT listening, where it clearly made a difference.
I should have explained more clearly, perhaps, that the new speaker stands have introduced both depth and solidity to the bass from the Q300 that was not present on the previous rather lightweight stands. I believe this is a common experience on many types of bookshelf speakers when the stands are upgraded. I have also, incidentally, learned that high quality stands are much more critical to getting the most from speakers than I realized.
When using the speakers in stereo, I now often switch the subwoofer off as the Kefs are doing well. I was not happy doing this before the new stands came into play. I try to avoid heavy bass as it unbalances the overall sound field and some jazz recordings are naturally bass heavy so the subwoofer has to be adjusted and it is less bother to simply switch it off.
When using them in 5.1 mode, they are crossed over at 80Hz and then I switch the Sub on to fill in the bottom end.
Obviously small boxes have a limit to what they can push out but the Kefs are amazing for their size. Ultimately personal preference matters and not having heard the JBLs, they may well be better for some people.
The actual point of my post though was that whatever the OP bought or is still to buy, he should make an effort to ensure solid stands are used.