What puzzles me you don't want a "normal" external audio interface, because you don't need any of the features.
Why are you using SONAR then for live performances, if you don't need any of it's features either? Isn't it an unnecessarily heavy program to be used only as a VST host? I wonder if using a plain VST host would affect the latency as well (?).

Kalle Rantaaho
What puzzles me you don't want a "normal" external audio interface, because you don't need any of the features.
Why are you using SONAR then for live performances, if you don't need any of it's features either? Isn't it an unnecessarily heavy program to be used only as a VST host? I wonder if using a plain VST host would affect the latency as well (?).

I tried other DAWs and I could not get any of them to work with the Ivory VSTI. They just wouldn't detect the DLL. I also developed a custom MIDI VST myself in .NET for some unique filtering features I needed and again only SONAR detected it. Tried Ableton, and a few others and I just couldn't get them to work with them. Also SONAR has some nice MIDI editing tools for accompaniment which I use for live play. So I use many of SONAR's features but I just don't use it for recording any live instruments, synths, or vocals. I mix recorded MIDI with pass through live play to drive VSTIs for live output. So low latency is paramount.

Sanderxpander
But I thought you didn't need/want 4 analog ins and outs? The Scarlett 2i2 is half the price and I don't expect a large difference in quality. It doesn't have midi though, the 2i4 does (and is still cheaper than the Komplete).

 
I don't but there isn't anything else I found to choose from. The Scarlett 2i2 is not quite half the price. $150 vs $220 and from benchmarks and forum testimonials the Komplete Audio 6 seems to have a lot lower latency. The MIDI is nice to have too since that's what I use mostly. So this is the closest compromise.

Right, it's 128 vs 229 here, so nearly half. But that sounds like a good consideration then.
Although honestly, if you really want top quality and would like a PCI based solution, I'd save up the extra hundred and get the RME 9632. At least it's 325 here. Benefit is also you can expand it later, they make custome expansion boards with 4 ins and or outs, and it has ADAT for another 8 I/O. It's the pro solution vs the prosumer solution.
Of course, you couldn't bring it with a laptop like you can with the others, and perhaps you feel it's overkill for your situation.