This was my question exactly a few months ago! I too, was looking into an Apuresound cable but came across a head-fi member Chris_Himself who produced a cable for me (I purchased the ER4P adapter on ebay for ~$30 that the cable plugs into which THEN plugs into the transducer of the ER4P). It cost just over 1/4 of the price of an Apuresound cable and sounded EXCELLENT - MUCH improved lows, and the highs/mids were more pronounced (tough to imagine with the ER4Ps) - this is amped of course.
Now to the amp - I didn't personally care for the Alo Rx MKII with the ER4Ps (you can check my profile for music preferences etc.) I DID have the TTVJ Slim w/DAC which I traded for the MKII and missed dearly!! It really brought out the mids of the ER4P, highs were just as clear/pronounced, and the lows were brought out just a bit more as well. If I could re-trade for my TTVJ SLIM I definitely would.
Now, my portable setup is my iphone 4 with LOD (just FYI - I personally think spending too much on an LOD isn't necessary - you could go with just a FIIO for the time being or get someone like Chris_Himself to produce one for you. I've had great success with Chris_Himself as well as another individual FONEBONE from singapore - definitely quality stuff fro a great price. Oh - back to my setup: iphone 4 w/LOD to Headstage Arrow 3G to ER4P recabled. This setup is just MONEY to my ears for portability, sound (the Arrow 3G has kind of a darker sound which kind of tames the ER4P (silver recabled).
Keep in mind that I, too, am a newbie to all of this, so my descriptions and subjective assessment of sound may be off, but I know what I like and I currently like what I hear. Definitely let me know if you have any questions!
