I would agree that the RC-70s are the way to go. They are a big step up from the RC-50s. A true 3-way speaker with great midrange and good bass extention. The center is also very good 3 way with decent sized drivers and enclosure. Check the size to make sure it will fit where you want to put it. I would find a way though as having a good center is very important.
Have heard these Def Tech before and not impressed. For the price they are ok where as for the price the RC 70s are outstanding. I had RC-70s until recently and when I bought them 5 years ago at (1250 each) I thought they were good value at the price.
I really liked the ML 12 when I heard them at Magnolia. They were one of my favorites there even when compared with higher priced BW speakers. I like speakers with very clear sound and detail which the ML had. Still preferred the Energys though.
Sorry Commsysman, had to smile when you said "But the RC-50 is not bad." LOL I know that energy speakers in general are not to your taste but nice to see you have seen the light finally and realised the RC series is "not bad"