I'm running all 64 bit. I tried to get SI Bass Guitar to work, but for some reason it wont.  I see that the MIDI is coming into the MIDI track, it even records. However, there is a disconnect between the midi track and the SI Bass Guitar synth. The chain looks like this
DR-880 MIDI --> MIDI SI-Bass Guitar 2 --> SYNTH SI Bass Guitar 2.
It just appears as though the synth is not seeing the input for some reason. 
 
THUS, makes me wonder, does this synth not work in 64bit mode?  And if not, what would be the next best synth to use?  I though about Dimension Pro or Rapture, but looking at the interface on those plugs are a bit over my head.
 
 
Any suggestions?
 

Went ahead and used Dimension pro.  Having said that, it does not seem to interpret the midi correctly. It's only reading 1 midi particular midi not out of the bunch in the midi clip. 

SI bass should work. It's native 64 bit so there should be no bridging issues. Its very good too, particularly if you route it through an amp sim. It was my goto bass for some time before getting Scarbee and Orange Tree basses for Kontakt.
 
How are you inserting the synth? There are several ways of doining it. I usually go to the Insert menu, when the "Insert Soft Synth" options appear I have Midi Source and Synth Track folder ticked and All synth audio outputs stereo ticked as my default. All the routing should then be set up automatically.
 
Another thing to look for. Are your MIDI notes outside the range of SI bass?  Try playing further up the keyboard, does it work. If so transpose your midi up one octave.
 
The other best choice for bass guitar would be Dimension Pro, there were however a few out of tune bass patches, so if you hear something a bit off, you know why. One of the free expansion packs added more bass patches to compensate for this. Dim Pro has a lot of parameters but if you are not up to tweaking you can probably get away with just loading the presets.
 
If you want very simple check out Cakewalk Sound Center which is imcluded with producer. There is an inexpensive expansion pack http://www.store.cakewalk.com/b2cgbp/ProductInfo.aspx?productid=10-DSBS1.00-20E
 
 
 
 

redbarchetta
Went ahead and used Dimension pro.  Having said that, it does not seem to interpret the midi correctly. It's only reading 1 midi particular midi not out of the bunch in the midi clip. 

What is the source of your MIDI data? If you are only hearing some of the notes there are three possibilities.

• Notes are outside the range of the patch in Dim Pro.
• There is Mult channel data in the clip.
• Velocities for some notes are set to zero.

The first two are common issues if you have down loaded MIDI files from the web. Often one needs to transpose the bass part up one octave.

redbarchetta
I'm running all 64 bit. I tried to get SI Bass Guitar to work, but for some reason it wont.  I see that the MIDI is coming into the MIDI track, it even records. However, there is a disconnect between the midi track and the SI Bass Guitar synth. The chain looks like this
DR-880 MIDI --> MIDI SI-Bass Guitar 2 --> SYNTH SI Bass Guitar 2.
It just appears as though the synth is not seeing the input for some reason. 
 
THUS, makes me wonder, does this synth not work in 64bit mode?  And if not, what would be the next best synth to use?  I though about Dimension Pro or Rapture, but looking at the interface on those plugs are a bit over my head.
 
 
Any suggestions?
 

SI Bass works fine here all 64 bit as well.  The MIDI track in Sonar is set to output to the SI Bass correct?
 

The source if the Bass MIDI is my Boss DR-880.
The MIDI out for the Bass in the DR-880 is set to channel 2. So I would think there is only just the one.  I set the input to the MIDI track to the DR-880 Channel 2 so it would only get the bass midi notes.
In both cases with both Bass SI and Dimension Pro, I set the output of the MIDI source to the synth, i even double checked on both synth tracks that it's input was the midi source track.
 
This makes me wonder, as with a drum map, do I need some kind of bass map as well?

Glyn, you were right. I pulled up the piano roll, started playing notes on the piano, it is out of range. So, going to have to move everything up an octave.

There might be an adjustment in the DR-880 or try adjusting the key offset in the Inspector, the top slider pointed to by "P" in the illustration below from this page
 

Thanks scook, I'll remember that for next time. I did it the manual way in the piano roll.  Lassoed all the notes and moved everything up one octave in one swoop.
 
 

I tried to suggest S.I. Bass Guitar on another forum,and I got the distinct feeling not many think it's very good,well I think it's fine,and yes I'm full 64 bit and all the S.I. work fine,though it is listed in the x86 part of Windows programs,on both my W7 machines.
Bob