It does seem either r-09 or H2 works best with external preamp. However, the H2 has very limited LINE input level ability before distorting, the R-09 does not have any of this limitation.
Consider the following:
H2 maximum LINE input level is a very low -1.9 dBu at maximum working #100 REC level adjustment. This makes it likely to easily get slammed with most any external preamplifier on today's market, and requires an external attenuation of 6-12 dB with external preamp connected.
R-09 will work well with up to +16 dBu input level, requiring no input conditioning with most any model of preamplifier. See tech review of R-09 inputs at:
www.sonicstudios.com/r-09revw.htm#inputsWith external preamplifier, the H2 does a reasonable job
very similar to R-09 as shown below in the noise plots.
R-09 plot is less easy to view (below), but look at external pre (green) verses R-09 internal pre (yellow) to get similar-to-H2 test conditions