I have the 6i6 and yes it's a great unit. The 6 inputs are
2x XLR multi
2X TRS line/Intrument
1X SPDIF stereo
MIDI in / out
This configuration is perfect for my set up and this is what you need to also consider. To many people buy interfaces and don't really think about how they will use it.
If you are going to need 4 mike pre amps then the Tascam is worth a look. Here's my blurb on features to look for.
http://www.cactusmusic.ca/Articles/Johns%20Audio%20Interface%20blurb.rtf So make a list of the features you find important. One guy here started a spread sheet to compare features.
I have a Yamaha digital mixer so SPDIF is a must. I also have a Joe Meek pre amp and TC Bass pre amp so I need the line inputs. Focusrite pre amps are good but my guess is the Tascam pre amps are something I'd like better.
I also have a Tascam us1641. I had to ditch it because of the driver performance, otherwise I'd still be using it. Another member was having issues with a us1800 and so I ran a loop back test on mine. It was off by around 800 ms
I then tested my Scarlett and it's timing was right on. A looback test is worth it for all DAW users.
Read this thread for details.
http://forum.cakewalk.com/Think-its-time-to-give-up-on-my-Tascam-US-1800-m3163904.aspx I know these are old interfaces but the drivers were just released in December. So your right to be concerned about the drivers and I have asked if any owners of the new Tascam's could run the loop back test and see if this is resolved. I like Tascam gear and am hoping they do get the driver issue sorted. I think it's getting there.
And the small amount of offset would go unnoticed by most people. But it's enough to drive me bonkers when trying to overdub bass for example. Ever note you play would be printed 400 samples early. The us1800 guy was getting 2,000 samples. And buffer size makes no difference. This is the driver reporting to Sonar.