H-IPS subpixels are shaped like ||||| and S-IPS are shaped either >>>> or <<<< . I could be very wrong, but if Hitachi and LG are the only IPS-panel manufacturers, then H-IPS is LG's proprietary IPS tech.
However, when it comes to 6-bit and 8-bit, the main difference (once again, I think) is that the 6-bit has to dither to display a full 16.7 million colours - the significance of that number? I beleive its the RGB colour gamut. The 8-bit does not have to dither, as it can display 2^8*2^8*2^8 which is approximatly 16.7 million; the three 2^8s come from the red, green, and blue subpixels (methinks).
And why does it seem like a TN panel? Well, the fact that it is 19" could be the reason. IPS that performs well is generally in the realm of people needing colour accurate monitors to work with either large images or HD video. The 1280x1024 (I think) rez of the Iiyama may not be good for large image or video work; even SD video practically needs an HD monitor to work with the tools, etc. The market for small monitors is not good, since viewing angles really begin to count in around the 24" and up; smaller monitors often do not have the colour shift over area problems that larger ones can. For example - there is only one big TN monitor model (28" Hanspree and its variations) that does not have noticeable colour-shift.
If I'm wrong, somebody correct me, but I'm 95% sure on displays...