Some info which may help in overall understanding of the sound sets...
The first Kross had 112 mb of sample data which included 421 non-drum multisamples (6 stereo); current Kross comes with 128 mb of sample data which include 496 non-drum multisamples (7 stereo), and you can load in additional downloadable sounds (already installed in some versions), which are OASYS piano (90 mb), four additional EPs (17 mb), and EDM (16 mb). Engine is EDS-i. Kross oscillators have up to 4 parts. Max polyphony is 80 on the original, 120 on the current version. Note that some individual sounds on Korgs can use up to 4 units of polyphony. So for example, in the original Kross with max 80 instances of polyphony, the main piano sound had 20 note polyphony.
Original Krome had 3.8 GB of sample data which included 583 non-drum multisamples (12 stereo). I am pretty sure it was broken down like this: 2.8 GB for piano (scaled down version of Kronos piano), 600 mb for EPs (sampled versions of some of the modeled EPs in the Kronos), 150 mb drums, and 256 mb for everything else. Krome EX adds another ~200 mb of sample data, with a focus on EDM, ethnic, and "hollywood production" sounds, and additional piano, bringing the total to 728 non-drum multisamples (44 stereo). Engine is EDS-X. Krome oscillators can have up to 8 parts, instead of the 4 of the Kross. Filter and EQ functions are more advanced than the EDS-i of the Kross. Max polyphony is 120. From one user evaluation I read online, the synth sounds between Kross and Krome seem largely identical, but the acoustic instrument emulation is better on Krome.
PA700 uses EDS-X + DNC. It comes from Korg Italy rather than Japan (where the Kross and Krome are from), designed by a different engineering team, and the exact differences in the underlying capabilities and specifications are a bit harder to discern. Polyphony is 128. There are numerous functional differences (besides the arranger functions you don't care about and obvious things like speakers, etc.). For example, Kross and Krome allow you to split/layer 16 sounds, and assign up to 5 insert effects, whereas PA700 only allows you to split/layer 4 sounds, and assign 1 insert effect (there are other insert effects reserved for accompaniment). OTOH, Kross does not provide any facility to switch from one sound to another without cutting off any held/decating notes of your first sound, the PA700 does have that facility (I'm not sure whether the Krome has any facility for that). The PA700 includes a drawbar organ facility which Kross and Krome do not (though honestly, it's not great sounding). You can load up to 256 mb of your own additional sample data to the PA700, vs. none in the Kross/Krome (though there was an unsupported hack to add a small amount of sample data to the original Kross, IIRC.)
My impression is that PA700 has less sounds
It's really hard to compare number of sounds, but in terms of factory Programs, PA700 has the most, at over 1700. If I'm reading the specs correctly, not counting drums, original Krome had 640 factory programs + GM2, Krome EX has 896 programs +GM2. (GM2 = 256) Original Kross had 256 factory programs + GM2, current has 768 + GM2 + 96 in the additional downloadables. But to elaborate on why it can be hard to compare these numbers, the 96 in the additional Kross download are 32 for the OASYS piano, 32 for the new EPs, and 64 for the EDM. So you have to qualify this with, how many sounds are just minor variations or recombinations of the same sounds, and how many of the sounds you'd find usable. I mean, is the OASYS piano download really 32 new sounds, or 1 new sound, or something in between? How useful are all the EDM sounds, if you don't use those kinds of sounds? Which also gets back a bit to what you said about quality vs quantity... it's also a matter of usability of particular kinds of sounds, which can vary from one player/genre to another.