For the most part, I think we're talking about the stock 1/4 track heads since Dolby B was seldom used with 1/2 track 1/4 inch tape. There are of course, some folks who have 1/2 track 1/4 inch Dolby encoded production masters which were used to produce commercially available 1/4 track tapes but those are pretty unusual.
Regarding the gain, there are a few Dolby B tapes that are duplicated at some pretty low levels (presumably to gain more headroom and dynamic range). I've found that some prerecords do have enough level to be properly decoded with the Dolby units I mod but some do not when fed with a tape head amp with 50dB gain. I'd feel better if the amp had more than 56dB gain with most 1/4 track heads that I've tried.
So, I don't think I can recommend the Seduction/Quickie for use with my Dolby units.
Now the Eros with a boost from a Quickie is probably an excellent fit. In fact, I think that the Eros Tape Head Amp is an incredible bargain. It can be easily upgraded with better parts as funds become available.