But like I say, make a list of your projected needs!
If your going to buy a mixer then 2x2 is possibly not enough. You'll want rear panel line ins too.
the 2i4 doesn't have SPDIF which is super important if you find yourself with a good pre amp or even monitors with that option. I repeat- For a few extra bucks the 6i6 has way more going for it than the 2i4. The mix control software is worth the extra $30 alone.
I run 2 mixers, one analog and one digital.
I use the 3/4 in and outs to the analog mixer used for my old MIDI gear.
I use the SPDIF in/out for my digital mixer which gives me another 16 mike inputs, monitoring control and DSP efxs and compression for both monitoring and printing to tape.
I also need the MIDI ports.
And as I said a lot of people report issues with buss powered interfaces introducing noise into the system.
Make a list trust me.