@adi74 to deal with your questions. Firstly unfortunately I will not be able to do the old/new Dragon comparison as my old ones are 20A and dedicated to my amps, the new is for my pre-amp (or if need be somewhere else in my digital stack).
I would not try to read back to the WEL Sig however as the changes to new series are much more about the design and geometry -- don't worry I'm sure that at least on the dimensions of information retrieval, dynamics and speed the Dragon will come out on top. I cannot answer however if this will be the mix you need. My recommendation would be to have the dealer you are working with provide both Firebird and Dragon and see for yourself -- everything else is speculation.
One dealer that can do this for you, and is well worth calling in any case is Randy at Optimal Enchantment in Santa Monica -- he shifts loads of AQ stuff and really knows the line and he is the one who originally set me onto this line of products