As you see from my specs, I am using a VS-700 console and I/O.  Normally, I set the ASIO buffer low when when tracking (slider value 2, 64 samples) and high when mixing (slider at 8, 1024 samples).
 
Yesterday, with the ASIO buffer at 1 (48 samples) the latency was still so distracting to the singer on fast passages, that I had to turn the vocal off in her headset.
 
How can I fix this?  It was not the singer's imagination.  It sounded like slapback to me.
 
I need to get vocals on six more songs for my publisher so it is somewhat important.
 
THANKS!
 
PS I have a brand new MOTU 896 mk3 I've never in the rack, but unless I am sure that will help, I hate to rewired the studio and change all the drivers. This seems like a software issue.

It sounds like you had the input echo button turned on.  I'd check that first.

Assuming you want to monitor through the DAW (IOW input echo on), if typing "E" or toggling the FX button in the Mix module removes the latency, the problem is due to plug-in delay compensation. Either track with effects bypassed or try the PDC button. The X1 help is not on the website but these are similar:
Mix Module
Live input PDC override

What options are there besides monitoring through the DAW?
 
The only effect on the vocal track was a reverb send which I disabled.  The other tracks had all been frozen or bounced to WAVs.

Tracks being recorded do not have to be monitored through the DAW. Most interfaces offer a way to directly monitor inputs while listening to the previously recorded tracks from the DAW. This is what interface makers call zero latency monitoring.
 
Simply disabling a plug-in does not remove PDC. The FX bin must be bypassed to avoid having SONAR add PDC for the plug-ins. Shortcut "E" and FX button in the Mix module bypass all FX bins. There is an option in the FX bin context menu to bypass individual FX bins.

If anyone knows how to hear inputs directly through the VS -700 while listening to the recoded tracks, that would be great. That is what I was hoping for.

I believe the VS-700R has direct monitoring. It is accessed through the software control panel called Direct Mix.

konradh
What options are there besides monitoring through the DAW?

the vs-700 provides zero latency direct monitoring capabilities. i used that for years and it worked fine. there is no reverb available when using direct monitoring (but some singers prefer dry anyway); if you use that, disable input echo in Sonar otherwise you will have doubled vocals (no matter what latency you set because direct will always be faster, Sonar always require some latency).
 
the other option is to go with lowest latency possible (i.e. freeze tracks, use cpu light reverb only) and use monitoring via Sonar (input echo on), but in that case disable direct monitoring on the vs-700 (make sure everything is muted or send to a different output in the vs-700 I/O GUI) ... it can still happen that the singer feels her voice doubled because she may hear it first in her head and then delayed in the headphones ...
 
option #3 is a mix of both options (which i also used successfully): use direct monitoring for zero latency, keep input echo for vox track off but also send the singer some blend of the reverb bus into her headphone mix ... this is quite neat as she will always hear her voice without delay in the direct monitor mix but still get some reverb effect afterwards (which is of course subject to some latency but that practically does not matter)

That is pretty much how it is done regardless of the hardware.

Since it hasn't been mentioned specifically - some plugins will add latency even when they're not on the track you're monitoring. Impulse based reverbs, look ahead limiters etc.

If the monitoring path itself (including all buses and sends) is "clean" of such plugins, using the PDC button should remove the latency.