IMHO, if you really want more dynamics than you can get out of a D400 you need to get new speakers, not new electronics. Lack of dynamics is inherrent in the design of the quads.
Now, if you really value midrange presense and body, as you say you do, you're not going to find it in any SS amps I have ever heard, with or without tube preamps, with my Quad 63's.
Frankly its hard to imagine anyone who cares enuf about the quality of sound reproduction to spend the loot to get Quad 989's to then want to use SS integrateds, of any quality level. But then, as Viridan implies, I doubt that is why you posted in the first place.
Now, if you really value midrange presense and body, as you say you do, you're not going to find it in any SS amps I have ever heard, with or without tube preamps, with my Quad 63's.
Frankly its hard to imagine anyone who cares enuf about the quality of sound reproduction to spend the loot to get Quad 989's to then want to use SS integrateds, of any quality level. But then, as Viridan implies, I doubt that is why you posted in the first place.