#1
On the TASCAM US-144 specifications it says it can record two tracks at a time, my question is, can it record two tracks (guitar 1/4 trs and mic xlr for example) into two seperate channles?

Also, can the PreSonus AudioBox US and Line 6 TonePort UX2 do this as well or can they only record one track at a time?
#2
usually when you have two types of input for each channel you can only use one of those inputs at one time.
If you need more inputs, get a larger interface.

Firewire can hold more data at one time and therefore it used on larger interfaces where you need to send more than 2 tracks to the computer in one take.

Download and read the manuals of the interfaces before buying them. It will answer many of your questions....As well Tweaks Guide, (linked in my sig)