PK2 earphones are the low impedance version of PK1. Although not as good as PK1, PK2's sound signature is similar to PK1. You don't have to drive PK2 with an expensive head-amp. If you are looking for something with high performance/price ratio, PK2 might be the best choice.
“ These were my sweetest sounding head-gear yet. It would be brilliant all-rounder if it would not require a portable amp for portable use. This is the first reason i left it, otherwise i almost got an ear infection from those foams.., they get dirty in a few weeks of massive use. I recommend them to clean, i boiled them in water. ” --angevoi
“ Well firstly this is not a true iem. The sound is about as great as one could get from an earbud. In my limited experience and without trying the pk1, I would say these are the finest buds you can buy. With that said, these are not for everyone, this is a niche product within an already niche market. I find driving it with my D12 anaconda makes for a pleasurable sound,...” --Jamesdeandoa
“ The PK3 is a great, warm earbud. It does vocals especially well because it is very mid-focused. It has impressive bass extension, not especially strong impact; the trebles are smooth and may roll off too soon for clarity and detail nuts. But the mids are what the PK3 are all about. ” --kmhaynes
Original HTC 3.5mm Stereo Headset Headphone for HTC One HTC Butterfly HTC 8X 8S MAX300 T528 X920E 802W 802D ONE M7 BLACK RED
“These cans come free with HTC phones released in the past year. This version, known as the MAX300 in China, can be found online for under $15 (as far as I know, they're not sold on most of HTC's online stores except China or Taiwan). There are also Bluetooth and three-button in-line versions being sold officially on HTC's site. Design The design is reminiscent of Beats headphones....” --FYLegend
“ Overall I have been satisfied with these phones. I would not recommend paying full price for them like I did. ” --Skoch