I agree with Kees' and Arny's comments. I'm not a replaygain or volume leveling expert, but with that stated, here's what I know that might help:
1) Replaygain as currently implemented in foobar2000 implements the EBU R128 and related specs, with one exception that I know of (which I'll note shortly). I know of nothing better for dealing with perceived loudness issues. I ran Replaygain just as a check to see what it said after seeing Kees' comment.
2) The track peak is a percentage of full scale for the higher peak on the left or right channel in these cases (don't know what it does for more than 2 channel). The peak value is just FYI - the peak value calculation shown does not affect the gain calculations. The peak info can be used for other processing to deal with potential clipping that can occur after applying positive gains.
3) The track gain is the volume adjustment performed by a player that understands and uses Replaygain track gain adjustments. It's an adjustment that was calculated to the reference volume of -18 LUFS. This is the only area that I'm aware of that deviates from the EBU R128 spec, which calls for a reference volume of -23 LUFS. This causes zero problems: under any circumstances you just need all the songs you want to level to have their gains calculated referencing the same reference level.
4) This is where it gets interesting. I don't know why there is about a 0.2 dB difference between the CDDA and HR files, and thus I don't know what to recommend. Since the Replaygain track gains for the HR files are consistently about 0.2 dB less than the CDDA track gains, this means that the HR files are about 0.2 dB louder than the CDDA files prior to any leveling, according to the perceived loudness specs of EBU R128. I also note that, to the best I can understand in reading the EBU R128 specs, there is no filter in the volume leveling processing to limit high frequency content in the calculations, so frequency content above 22k will be accommodated in the loudness calculations. So I see 2 possibilities, but there may be more:
a) As Kees noted, perhaps a 0.1 dB offset was introduced with each resampling or processing step
b) Since the energy spectrum below about 22k is (presumably) identical in each version of a song, and since the HR version has additional energy above about 22k, it seems possible that the HR song could always be perceived as louder by Replaygain or any other volume leveling processor that uses a perceived loundness calculation without a high frequency limit.
That the dB differences are about 0.2 dB makes me think that 4.a is the cause. That the dB difference is not exactly 0.2 dB in each case makes me think 4.b could be the cause. Or it could be a combo of the two. But I'm waaay out of my depth in even speculating what's going on.
Hope that helps.
Edit: perhaps TMI, but the formula I use to convert peak info to dB info is Axon's formula: http://www.hydrogenaud.io/forums/ind...st=0&p=715285&
. There are many pieces to the EBU R128 spec, but the main document I read that gave me the impression there is no upper frequency limit to loudness calculations is https://tech.ebu.ch/docs/tech/tech3343.pdf