Yep exactly. Set Input 1 to Mic, and Input 2 to Variax. I wouldn't bother with the Vintage Pre though, it's a hassle and prone to clipping (see relevant thread currently on the front page of the forum). You should be fine with just the mic trim knob on maximum, then some EQs and other effects. I use (in order):

• Studio EQ with just a 4 dB boost at 5kHz, and Gain at -4. The nice thing is you can use the Gain parameter in this effect instead of the Mic Trim knob, if you don't want to reach for it or just want to always have it at max. They'll do the same thing. I have the Gain backed off to -4 because there was some clipping, also to compensate for the boost. The 5k boost is for sibilance enhancement ("s" sounds).
• Graphic EQ with 80Hz at -6, 220Hz at -1, 440Hz at -4, 1.1kHz at 0, and 2.2 kHz at +4. This takes away some of the boom and mud, and also enhances intelligibility at 2.2k ("sh" sounds).
• Mid Focus EQ with HP FREQ at 5%, HP Q at 50%, LP FREQ at 90%, LP Q at 50%, Gain at 50%. I am essentially using this as a high pass & low pass filter, not really filtering off very much, just the edges of the spectrum.
• Analog Chorus with Speed at 1 Hz, Depth at 50%, Tone at 50% and Mix at 50%. The chorus fattens up the tone a little bit, basically doing what a Pre would do but much cleaner. Play with Tone to get slightly different sound here, it's a very subtle effect.
• Tube Comp with THRESH at 50% and LEVEL at 10%. Be careful with this one, if you have speakers on while using the mic and the mic is played back through the speakers, the compression could generate awful feedback. Either go with headphones, or start off with THRESH at 100% and slowly bring it down while testing it to make sure you can get to 50% without feedback.

The way I placed these was, the 3 EQs and the chorus go before the "amp" slot (which should be empty), and the Comp goes after the mixer. This should force the signal from left mono into stereo (the comp does that if you have a one-sided signal and you place the comp after the mixer). I advise against selecting Mic or Same on both Inputs, it gets very noisy as it just doubles the signal, just set one input to Mic and one to Variax. It could also be set to Guitar provided that you don't have a guitar or a cable plugged in that could potentially generate noise.

Keep in mind these settings are for a Shure Beta 58A, and the specific voice I'm working with. For your mic, you'll play around with the various EQ, and if it's a quieter or louder mic, you can use the Studio EQ Gain parameter levels to adjust things. Good luck, and please let me know if you come up with a better signal chain (especially if you manage to use Vintage Pre without any distortion)!