The network's press release is
here. The overall household increase is the smallest number, with bigger jumps for total viewers and demos. GSN skews so old - a median age of 57.5 in prime time prior to Amazing Race, and a timeslot median of 54 prior to the show - that almost any bump in 18-49 or 25-54 would produce a big percentage increase.
The network gives a 350K total viewer number, and the .40 rating would translate to about 230K households. Again a modest household total, but the younger demos mean more viewers per household. That's always been a problem for the network.
The show still has an incompatible lead-in. Backtracking from the pre-Race numbers the network gives - 57.5 for all prime time, 54 for the 9:00 slot - Millionaire's median age is probably pushing 60. Iti's sources and some published bits of information indicate that Millionaire is getting about a 0.5 or 0.6 household rating compared to Race's 0.4.
What seems to be happening is that some of Millionaire's oldest viewers are switching away, while Amazing Race is pulling younger viewers who are not big fans of Regis' show or traditional game shows in general. It's possible (but not a cinch, of course) that Race would do better with a more compatible lead-in. But Millionaire isn't going anywhere after the renewal and the licensing of additional episodes.
At any rate, there really does seem to be a sea change in GSN's audience at 9:00, from Millionaire's median age near 60 to Amazing Race's median of 42. How this plays into GSN's decisions on future programming will be interesting to see.