its might not be an answers to your questions but i thought i'd share experiences, maybe you'll get something out of it.
Currently i'm using mixxx with vinyl control with turntables, an external mixer and a m-audio fasttrack ultra 8R (8 I/O which i already owned for making music). My mixer is a PMC-05Pro3 DX, you can see it here: http://www.vestax.com/v/products/detail.php?cate_id=152
. It's an older (discontinued) 2ch mixer and it has two switches on the front that allow you to send the signal (in this case the timecode) from your turntables straight to your soundcard thru 2 outputs on the front of the mixer. Next to the outputs are inputs that will put the signal from your timecode (in my case mixxx) into the faders of the mixer. This means i can mix regular vinyl and/with timecode just by flicking those switches. I configured the decks in mixxx to separate outputs on my soundcard, 3/4 and 5/6, which are connected to the inputs at the front of the mixer. When i want to play a wav/mp3, i use a timecodevinyl and mix with the mixer (just as a regular vinyl) and i don't use the faders/fx/master/recording in mixxx at all. (I already made a skin for me without al those things) When i want to record a mix i just record what comes out of my mixer, otherwise you get the mix with the timecode tone.
As for the question why one should do this... In this way i can play my just-made track very easily and in a way I'm used to. In my case i already owned a nice collection of regular vinyl and a soundcard with multiple in- and outputs. Mixxx and digital mixing in general is an addition for me, my startingpoint was straight beatmatching (..well years ago
). I think, for me, there wouldn't be a reason to use an external djmixer for mixxx if i hadn't already had the bulk of the gear that is needed for it. For me the final choice came down to a solution with external audio paths, cables and turntables or a kind of all-in-one, laptop and midi controllers. My guess is that things in between that are so personal and specific that you'll have to find/make that yourself.
I own a akai lpd8. Its has 8 pads and 8 rotary knobs, NO faders and is usb powered. Very handy, little thingie, but the knobs aren't really sturdy I want to use the pads for selecting/loading tracks in the playlist, but haven't had the time to make the script for that yet. I don't think it would compete with the mpd18 and/or xsession. Especially the xsession, because its made for dj'ing purposes
so... i guess a very long answer to a question that wasn't asked