"Definitive" is a tricky concept. There's far more subjectivity involved in it than the word would imply; definitive of what, to whom?
Nothing is odder than listening to the fans of various performers debate which is the "definitive" recording of a certain piece--a debate which simply would not occur if any of the available recordings were objectively definitive. Sometimes a composer's own recordings don't make the grade because some other way of performing his music has convinced the listeners more than the composer's own conception of it (e.g. Fritz Reiner vs. Richard Strauss conducting Strauss' tone poems).
But back to the subject, you might want to consider that Schoeps makes a portable preamp for their microphones, the VMS 5U; some people here use it and like it a lot. Of the studio (rack-mounted) preamps you mentioned, I would pay special attenion to Millenia Media. Another name to consider, though you didn't mention it, would be John Hardy.
In terms of objective quality (measurable and audible performance) I don't consider the little Grace preamps to be middle-tier at all, despite their popularity among advanced amateurs. For my own portable recording, mainly with Schoeps microphones, I often use a Lunatec V3. It's sonically transparent, completely reliable, has good metering, and its phantom powering is correctly implemented.
Edited later to add: Due to a misunderstanding about what was to become public information when, I failed to mention above that Schoeps is also introducing a two-channel, rack-mount studio microphone preamp called the VSR 5. It's based on the circuit which their engineers have used in-house for a number of years for developing, measuring and evaluating their microphones.
Edited even later to add: Sound Devices also offers portable preamps that have excellent input headroom (which you need for piano recording with professional condenser microphones), proper phantom powering and good rejection of radio-frequency interference. They're very rugged and well engineered for the real world.