When I had my Energy Veritas 2.3s, I had to use my EP500 with a xover of 70hz to get any bass action going on. Of course with that high of a xover, the bottom end in music was not quite as thight as bass coming from mains like M80s.
About a month ago I replaced my Veritas with a pair of Acoustic Zen Addagio towers. They also have 2 x 6.5 drivers but have a transmission line design with a large front port, they are also 48" in height and deliver outstanding bass response, so much so that I have turned off my EP500 for music playback. Now to be fair, after some more experimenting and with the advice of the great people on this forum, it was concluded that I was sitting in a bass null, which did not seem as aparent with the Veritas because they did not go as low as the Addagio, not even close. So, as mentionned before in this thread, positionning of both speakers and sitting location plays a HUGE role in weather or not you use a sub with your M80s, or other large and capable towers. Now that I have my seating 12" from the back wall as opposed to the 4 feet previous, the bass is absolutely amazing without a sub.
The only downside of me moving my couch from 4 feet to 12" from back wall is now the QS8s are ahead of me by about 2 feet. It's not ideal, but I can't move them back any further, I have listened to a few movies that way and it's not that bad, the QS8s with their quadpolar design still give a very satisfiying surround experience. For really critical movie watching, I'll just move the couch back to where it was.
