At this price level the choices can become overwhelming and I suggest you get to a shop where you can try a couple to see what you like as we all hear things differently. I also have the A&K Jr and right now I am listening to it with the FIIO EX1 and it sounds great. It also sounds good with the T-Peos 300's and a host of other earphones as well as some low impedance full size headphones. With the Jr I don't think you can really go very wrong as it is an excellent source and has synergy with many, many phones and it will be a matter of personal choice as to what sounds good to you. Again, if you can get to a shop that has demo units, I highly recommend you do so and listen to a number of different phones with YOUR source and YOUR music so that you have a reference point that you are familiar with. You may be surprised by your choice of phone once you hear a couple. Also, don't let price be your guide(within reason) and buy what sounds good to YOU as you have to live with it. I have a fair number(~20) of different earphones ranging from inexpensive to mid-priced and sometimes the difference between the inexpensive and expensive phones is not as much as you would think, then again, I have 60 year old ears so your mileage may differ. Your mood will also dictate how you perceive your music and also wether your ears are fatigued or not, so, as you can see, it is not a simple question to answer. The best is to listen to as many as you can and then purchase your long term phones. Prior to that, I suggest you shop in the 50 to 100 dollar market as there are many competent units in that price range(read the reviews) and then take your time about further purchases. I hope this helps and didn't confuse you too much. Cheers.
