First, your are not asking too much, what I write is only my option, but I happy to share it with you. The 421 came today and all I can say is WOW. Listening to it as I write this and I am hoping tonight never ends! Great amp, GREATER AMP COMPANY! I ordered this thing late Thursday, it was here today (Saturday) before noon, at USPS Priotity rate!!! Awesome!!!
So, for the amp. Depends on what your driving as far as headphones. For something like Grado 80's the Fiio 11 or JDS CmoyBB will make you smile. I have Grado 80's, Sennheiser 25-1-II's, and Sennheiser 650's. If I was gonna stay with the HD-25's or Grados, I would love the Fiio, or the CmoyBB even more. But to be happy with all three, it's the 421 , the other two amps just don't drive the 650's to the level I want.
Of course, theses are my opinions, based on my headphones and the type of music I enjoy. If your looking for head pounding, window rattling bass, none of these may be what will rattle your cage. For me, all three put a smile on my face. If you can afford the 421, go for it, it's the best of the three because of it's ability to be more versiable. The CmoyBB would be my second choice, very clean sound, third is the Fiio 11, great amp for the price and I'll probably keep mine as a back up. I'm giving the CmoyBB to my son. Bottom like, I like all three, but I'm keeping the 421 for me

. If I wasen't trying to drive the 650's I'd be very happy with the CmoyBB, it's a very clean sounding amp.
As far as LOD, it stands for Line Out Dock. It plugs into the bottom of your Apple device, just like the charger. It bypasses the devices amp, and gives you the cleanest signal into your amp. If you came directly out of the headphone jack, you'd be feeding an amped signal into an amp, YUCK!
For the Fiio 11 and the 421 I like the Fiio L-9, for the JDS Cmoy I prefer the Fiio L-3. Both can be purchased thru JDS, or for a couple of bucks less, Amazon. The 11 has a 90 degree line in plug, the L-3 a 180 (straight). Look at the volume knob on each amp and you'll see the choice that works for you.
Also, with the CmoyBB you may want to go with rechargeable 9 volt batteries, so by the time you upgrade, buy a charger cable, and the LOD, your at 100 bucks. So, Fiio 11 and LOD, around 65 bucks, CmoyBB 100 + bucks, C421, 180 +.
Your call, all will put a smile on your face, still lov'n the 421 as I write this.
However you go, enjoy!