HS is basically a shortened version of headset lol. ultrasone model names are pretty straightforward. if it says DJ, it was designed for DJ, if it says PRO, it was designed for audio professionals or audiophiles, HFI is their more consumer oriented stuff, and the icans are their portable headphones. as far as being different, the main difference is that the HS sets use different drivers, have a microphone, and the headset design differs considerably from the rest of their sets. i cant confirm for the HSD-700s but the HS-75s are closed ear/air, which means that they are semi shielded from outside noise and vice versa, where as some of the HFI, PRO, and DJ sets come open ear/air, which lets sound in from outside as well as letting the sound form the headphones out more, leading to a more natural sounding headphone, though some people prefer the closed sound. as far as quality is concerned, Ultrasone, all though being a bit of a lesser known manufacturer (vs Sennheiser, BOSE, Denon, KOSS, ect), they still make exceptional products. some people say the HFI sets seem a bit cheaply built compared to similar offerings from Sennheiser and other competitors, but the quality of the drivers within is always top notch German engineering.
as for my thoughts on the quality of the mic, trying to get it to work actually took about 2 hours, because it uprooted a major hardware conflict between the NF2 audio controller (which i forgot to disable in bios), and my X-Fi. after 2 system restores, a safe mode boot, and much pouring over system event logs, and a few BSOD, i got everything straightened out. i tested the mic over my 5.1 (Logitech z-5300E), my HS-75s, and my PRO 2500s, and i have to say that it sounds great, and picks up sound really well. i could whisper into it and it still had above par sound reproduction (compared to the $35 logitech headset i was using prior it was a dream). my final thoughts on the product:
after burning in the headphones and testing the mic, im going to give the product an all around 4.75/5, and i would also like to comment that the 4.5 i gave the headphone drivers earlier was actually not adequate, and im upgrading my rating to a 5. fixing the hardware conflict i had been having eliminated a major source of interference in my audio circuit, and the sound quality of the headphones has thus gone up in comparison to the PRO 2500s im rating them against. the only thing i think they are lacking in is the materials used in construction. they are REALLY light and comfortable which is wonderful, but the plastic used in construction of the set doesnt quite feel as high grade as what was used in the PROs. you also cant replace the earpads if you would like, which you can do on just about every other ultrasone model. apart from that, it was a sweet buy, and i would buy a second pair if these ones were ever to be lost/stolen/destroyed.