Deleted, the MX300 that I thought I had first choice on was sold.
 

Interesting. I have the MX200, and the USB VST interface only works with 32 bit systems so I I haven't bothered  to try it that way. Looks like the MX300 was given 64 bit drivers? This is not clear but they do say "any" computer. 
I use mine for live vocals and as a headphone mix sweetener. So dead simple to use and get a combo of any reverb and delay. The MX300 doesn't look like it's dual channel. 

 
This is the MX 200 you can see the 2 processors. For me it's perfect. I can change settings quickly. When I have time I will program pre sets and think about a midi foot controller or go whole hog and have Sonar ( or? ) send the midi. 
 

 
But it would have been cool to use it as a VST. It does seem to sound better than our free Pantheon. 

The 300 is a "true" stereo dual processor with mutli-mono output capability.You have to use the menu in order to get tot eh other processor so it is part of my "set and forget" rack.Great units the entire line I have the 200,300, and 400XL as part of my FX racks..Although I do not use the VST part of it It would be nice to tinker around with it.I use them pretty for the same thing as can sweeteners and for one particular client who likes his vocals baked with the FX.I tend to use them more than my PCM-60 and 70 now since they sound dated.Cheers.

From what I found on searching there are only 32 bit drivers for the MX300 too. 
 
Since I didn't get it and wanted some Lex reverbs I bought the software LXP Reverb plugin VST from M/F as it is on sale.
 
 
 

Ya but Jack, the rack mount unit looks way better!!! :)   

The VST graphics aren't bad.  It was cheaper than the used MX300, anyway.
 
Used one of the reverbs yesterday on a mix. 

So do you find the VST sounds better than the Sonar supplied Pantheon? 
I don't think that's too hard to achieve. 
 
I used mine last night on a vocal track "live" 
I used my Joe Meek 3Q's extra output to drive it and then recorded to a separate stereo track. 
It was so easy to get the exact result I was looking for and by automating the "Lexicon" stereo track I got the over the top part I needed on this one sustained part I do. And it is nice to sing and hear what will actually be close to the finished sound. I was using a deep reverb and long delay on a slow blues song. If you ever decide to pick one up, go for the MX200 with the dual processor. 
But anyhow this was a work around to using a hardware effects processor in a committed but not committed way. 
I think I too will consider the VST version if it compares to the hardware. 

I don't know if the Lexicon is better than others.  Just that I used it on a guitar track for that one mix.  I was really going through them trying the various programmed patches and the one I used sounded good so I used it.
 
 

I have the MX200 in my rack but only use it as an analog reverb unit for vocalist to hear reverb in their cans when singing.  It's a good reverb unit with lots of choices, but I never used the USB cable with the unit as I didn't buy it for that reason.