“Looking at the picture of the PK3's I wasn't expecting much. They look and feel cheap using a generic case for the drivers. First I tried them without the foam covers and they sounded awful. I originally thought I had been sold a pair of fakes but after using them with the full cover foams I am impressed. they have good definition and separation in the mid and high frequencies. The bass is...” --thebluebulk
“full review here: http://www.head-fi.org/t/689006/review-audiofly-af56 The earphones were given about 40 hrs. The AF56 are not just an improvement over the AF45 in design and comfort, but also, and mainly, in Sound. They offer a much bigger and very lively sound with better overall balance. Not unlike the AF45 model, the bass is very dominating. But...” --Zelda
“ 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
“If you want to read me ramble on more about haptics and finish quality, head to Ω image's review. I know it is a year on and this earphone is no longer en vogue. However, I reviewed it. Take that world! ARggggh! Why has it taken so long for me to get this on? Well, because I take a long time. Yes, even if the review is short. And I've sort of changed opinions on a...” --shigzeo
“Build & Design: Great. Audiofly chose to use very good materials for the AF45. They're available in four colors: Black, White and Black, Green Olive, and Brown. Starting from the straight plug, it's very sturdy and well relieved. The housings, while are made of plastic, feel very sturdy too. They are lightweight but a bit on the large side. As for the cable, it's a Y-cable and one...” --Zelda
“ 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
“ Overall I have been satisfied with these phones. I would not recommend paying full price for them like I did. ” --Skoch
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.