Well the time has come for me to say goodbye to the FIR Audio Frontier series. I've really enjoyed my time with them, they're 3 quite different IEM's! Thanks to
@Damz87 for organising and Minidisc Au/FIR Audio for the opportunity to audition these. My thoughts and impressions are my own and not influenced whatsoever.
Packaging and included accessories:
As this was a tour kit they weren't sent with the retail packaging, from what I've seen it looks like a very nice unboxing experience. Included tips do the job across the three, I ended up using the large silicone ones. They come with a 4.4mm balanced cable, no complaints with the build. For the price of these I would expect a 3.5mm cable to be included as well however i believe it's only the 4.4mm, as my preferred combo was with the Mojo2 this would be an added expense. You also get the Atom XS interchangeable Modules, I did not touch these as it's only a 1db change and didn't want to risk breaking anything. The look and feel of all three are TOTL, absolutely beautiful.
I did try some foam tips, however found that these generally accentuated the bass even more and none of these need that.
Commonalities:
Soundstage, amazing across all three. I think they're in this order: Ne4, Xe6, Kr5 but all are great. They do leak quite a bit of sound, my wife does have some super level of hearing but she did comment a few times that she could hear them quite clearly across the full frequency band. In terms of isolating me they were all equal in that they blocked out most outside sounds, no issues at all. Bass across all three is amazing, it's their standout feature. If you don't like thick detailed bass, none of these are for you. If you love bass, you need to try these out. They also all take EQ quite well, all impressions are based on non EQ'd sound.
Ne4:
I've posted my thoughts on this previously, to sum it up I found the Ne4 to be a great allrounder. I think it would be a perfect fit for someone who doesn't have a lot of other Head-Fi gear as everything you throw at it sounds nice - if I were to ever consolidate down to one IEM these would absolutely be in the running. They're not as detailed as I sometimes enjoy, however you can listen to them (as I did) for long periods without the slightest hint of fatigue.
Kr5:
My favourite of the 3. I've read the reviews of others and heard the feedback about the treble, I think between these and the Meze Advar I've learned that I like some spicy treble
You maintain the lovely bass of the Ne4 but also get a more detailed sound. Vocals sounds amazing through these, where they are a little recessed/veiled on the Ne4 they come through clear on these. Sound is (obviously) brighter than the Ne4. I'd say they're the closest to neutral, but with a bass focus. They're not going to be for everyone (as demonstrated by the other reviews), for me they are pretty much perfect. After I got through testing all three I landed on these and they really haven't left my ears much after that.
Xe6:
The top of the bunch (price wise), here we leave the Kr5 sound signature and return more to Ne4 territory. The bass here is the best out of the three, you really have to hear it to believe it. Extremely textured, with an amazing feel to it. Certainly doesn't sound/feel like an IEM. Vocals take a step back, I think that bass overwhelms the mids a little. Detail is also a step down from Kr5, above Ne4. From a bass presentation they're the best, for mids and highs I prefer the Kr5. I did really enjoy these, particularly for non vocal tracks, they just seemed like a step back for my tastes from the Kr5.
Across all three I heard bass detail that I've never heard before in tracks - quite an experience!
Where does this leave me for a recommendation? As long as you don't shy away from bass I think you'll find something to love here. With their price points, I wouldn't recommend a blind purchase unless you've read many reviews and really understand what you're buying, if I'd bought the Ne4/Xe6 blind I don't think I'd have been happy, if I'd chosen the Kr5 I'd have been over the moon - if you can audition them please do! For full disclosure, and to emphasize the above point, I assumed I would have preferred the Xe6 before I heard them all and would have been my blind purchase choice. For anyone with similar ears to me the Kr5 is the best I've heard and it get's a recommended purchase - after spending another week with them I think they're on top of the IEM mountain for what they offer. I'll see how much I miss them but have a feeling I may need to squirrel away some cash and buy them down the track
(I'm looking to use it on my EVO when I get them back from Empire Ears, the stock Rn6 cable is too good) 
