I typed the below before reading your update that you want to go with 8 channels now. I have no experience with the Tascam units, I do have experience with Focusrite and MOTU and they've both been great for me. The price on the Tascam worries me because it's so low, but that's based on nothing but assumptions. Do your homework and take your best shot - yeah?
I also inadvertently replied to Luke19Boarder's post above this one with my paragraph below starting with "Something else to consider...."
I was thinking that the EIE Pro would allow me the record drums sometime down the line as it's got 4 inputs. That would be difficult with only two, no?
Sorry I missed this question. Not really a matter of easier or more difficult, it's just a matter of how many options you want/need. If you have a good room and good sounding drum kit and a great drummer playing them, you can get great tracks with only two mics. Look up the "recorderman" or "glyn johns" methods on youtube.
Obviously with four you have more options. I'm using four mics for drums these days and I'm pretty happy and I'm recording in my basement so it's FAR from a "great room". But I have bass traps in the corners and the ceiling joists are stuffed with the pink fluffy insulation to reduce weird reflections. The drums are cheap crap drums, but they have okay heads on them and they've been tuned by a "real" drummer so they sound about as good as they're gonna for now.
I basically use the recorderman method with a pair of good overheads (AKG C414) and then I add a close kick mic (Beta 52) and close snare mic (57).
Something else to consider when thinking about the number of interface channels that doesn't seem so obvious until after you've had some experience: I'm generally recording alone so I'm moving from drums to bass to guitars to vocals and back again. So with only two inputs, I would have to re-connect EVERYTHING every time I move to the next instrument, then if I wanted to go back and re-do something on a previous instrument I would have to play cable-monkey and re-hook everything and try to guess about placement of mics and knob positions on outboard gear that was in the signal path and I'll never get it exactly the same and so on and so on.
I'm currently using a MOTU 8pre (8 channels) and that allows me to put four mics on the drums, one or two channels for bass and one or two for guitars and
leave everything setup like that all the time. Wow was that a revelation for me. Suddenly I could keep my head in the song for thew whole process instead of flipping back and forth from "artist" to "engineer".
Yet another consideration - is what kind of sound you're going for. Far-miking a kit (for example: capturing the whole kit with only two mics) requires fewer channels but also
sounds entirely different than close-miking a kit (which of course requires more mics) so depending on what genre and what sort of feel you're going for, one or the other might sound entirely wrong for what you're trying to accomplish. I would not suggest a two-mic, all-room-sound solution for a metal band - right?