K5 + X5SG: Docking is no issue and the player is immediately recognized. Direct from the player I need High gain with the HD650 but the K5 powers it perfectly on low gain. Like I mentioned before, the spaciousness when connected to the K5 is the most different. Next to that the K5 has a softer presentation where the X5SG directly has a closer presentation with a tad more body in the mids.
K5 + X3SG: Direct out of the X3SG, the HD650 also needs the High Gain setting. For the rest it basically is the same as the X5SG: the K5 has a smoother and more spacious presentation. I do prefer the K5 + X3SG’s bass and mids over the X5SG + K5’s. Voices out of the X3SG directly are also more forward where they’re more laid back in the K5. Some people have reported docking issues with the X3SG but I have no problems at all with it. (I’m not using the rubber stick-on things).
* K5 + X1: I quite like the HD650 directly out of the X1 as it has most body and the biggest bass. In my case the X1 only charges when docked and I can’t get the K5 to recognize the player in any way. The X1’s screen simply shows it’s charging. Paul’s X1 connected without any issues though as far as I understood.
EDIT Feb 19/2016: The reason my X1 doesn’t “dock” is because it is a trial-production sample and that hardware didn’t allow docking. The consumer/normal version of the X1 works perfectly with the K5 dock
The K5 has no impact on the RCA OUT-signal and as a result there isn’t a lot to say about the K5’s impact on it. Using the X7 as a DAC with my laptop was pretty easy but the sound “lagged” and that’s especially annoying when watching movies as the sound doesn’t match the image and you can see people mouths move without hearing the correct sound. It probably has to do with my settings but I haven’t figured out just yet how to solve this (it isn’t a priority to me either as I don’t use the X7/K5 in this way and for music it doesn’t matter at all). Paul got it working without any issues though, it’s probably my bad setup.
Sound wise the K5 is OK but when using my full sized headphones, the K5 doesn’t do miracles. The USP of the K5 to me is the docking ability for the Fiio DAPs and making your portable desktop an easy desktop setup where you can either use the DAP or use the DAP as a DAC for your pc (drivers needed for Windows).
I like using the dock with the X7 at work because it is easy, because it charges the unit and because I can use its DAC with my laptop. Purely looking at sound quality, I prefer the headphone out of the X7, especially with AM2 installed. If you need more power, the K5 is a good and cheap option, but power isn’t everything and it does show sound quality wise. AM2 which is going for more or less the same price might be a better option for those who don’t need the other possibilities/advantages of the K5 Docking station.
If you are interested in the K5 because you have one of the other Fiio DAPS and want to use the K5’s amp, I recommend demoing it. Take your DAP with you so you can hear the difference between the DAP and the Fiio K5’s amp yourself. I’m sure some will prefer the DAP’s amp over the K5’s and the other way round while others of course won’t hear any difference at all. From the other Fiio players (X3SG, X5SG as the X1 didn’t connect) I especially liked the X3SG + K5 combo.
Anyway, it’s great to see Fiio release a docking station with an integrated amp for this price. I’m sure a lot of people will love that they’ll get to use their DAP now as a desktop setup. Well done Fiio, even though there still is some margin for improvement in the amp section.