Can't make Index Selectable Multiplexer work!

I know I'm neglecting something silly, but I just can't make one of these infernal devices switch.  I need to select between two DC levels with a logic 1 or 0.  I've used ABCD blocks before with no problem, but figured this time I'd just use the Index Selectable Mutliplexer.  Here's my 'prove it doesn't work' circuit under two conditions:

In the top picture, the left ReadBack is showing a DC level of 1 and, sure enough, the full output of the DC Input Entry is switched through to the meter and the other ReadBack.  But then when I Mute the control lead, and the switching level ReadBack shows a zero, the switch should go to the other input and drop the level 20dB.  But it doesn't.  I've also tried by replacing the Mute module with a second DC Entry, programming it for a zero or a one, and still can't make it switch.  What am I doing wrong?  I read the Wiki for that Multiplexer, but it doesn't specify logic levels, etc.  Help!

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