Impact Twin dead and a new unit is required

As stated in the subject line, my TC Electronic Impact Twin is dead and I am in the market for a new audio interface. I really liked my Impact Twin but I am through dealing with TC Electronic’s poor customer and product support. Since I have used Cubase since VST24 and continue to use Cubase 7, I have almost decided to switch to Steinberg MR816 csx or UR824. I need the input or advice of those that own either unit. Ideally, I would like the input of those that have had the Impact Twin and have switched to either the MR816 or UR824. Here are a few questions, among many, I have:

1.) Are the MR816 or UR824’s converter’s as good or better than the Impact Twin?
2.) Beyond additional mic pres what am I gaining over the Impact Twins features?
3.) Everything under Cubase 7.0 (64-bit), Windows 7 PRO (64-bit), and Impact Twin was stable and without drop outs, glitches, or difficulty. With the most update MR Tools will I be having a similar status?

If I were to instead choose the UR824:
1.) Will I have any difficulty monitoring virtual instruments and recording audio with less than 30ms of delay? I routinely will use Superior Drummer 2.0 and Jamstix 3 running simultaneously while recording two channels through Amplitube 3 or a chain of 2-3 vst effects. This scenario was not a problem recording with the Impact Twin. However, I have heard for so many years that USB could not handle such a scenario without massive latency. I should note that I am running an AMD 6 core machine with 16gb or ram and 7200 rpm drives.
2.) I understand that the UR824 is relatively new but I would like to be able to use this machine for at least 5 years. Have there been any known defects that have been rendering these units useless in the last three years?
3.) The MR816 csx, is older, has anyone been disappointed by mechanical breakdowns of the units? Like I said, I would love to be able to not have to worry about known defects putting me in this position again for at least 5 years.

I would rather be making music instead of having to write these queries and TC Electronic has put me here. If anyone could help with insight into my two choices it would be greatly appreciated. I am aware of the the Focusrite Pro 40 and have ruled it out due to lack of monitoring dsp. I am also aware of MOTU’s offerings. I would appreciate insight just on the units I have questions about.