oh I thought the index was the index of the device input.  What I want to say is "if there's an audioinput specified for a deck > the current minimum, increase the minimum."  So like I have this line in my config:

  <input channel="0" type="Vinyl Control" index="3" channel_count="2"/>

That's the VC input for deck 4. 

Would it help to first check that the in type is deck, vinylinput, or extpassthrough?  all of those correspond to deck numbers, right?