You should seriously check out the Craig Anderton Gibson EB5 sample bank for DimPro. It sounds EXCELLENT and since he took the time to proper sample it with all the pickup configs it's pretty versatile for many styles.
 
It should still be in the Cake store and I think goes on special from time time (not sure what full price is but I don't think it's even that much anyway for what you get).
 
And I don't say this to boost Cake or my bud Craig. It's just a really good package for nice, realistic bass synthesis.
 
I play bass myself (almost as long as I've played guit actually) and usually play my own tracks but I've run the EB5 samples through various common bass effects chains (sims, compression, limiting, EQing, etc... I won't go into ultra detail about that) and it responds BEAUTIFULLY just like a really nice live bass track would. It cuts through a mix exactly how you want a bass to with minimal effort and as I said slides into pretty much most styles/genres.
 
I've only got to REALLY use it once for whole tune where the bass was entirely MIDI but it worked great.
 
What I'm going to be using it for is as bass "support" for my live tracks. Essentially play the part live, convert to MIDI using ARA (and clean up the resulting MIDI) then blend it with my live signal track.
 
Anyway... it's just a nice, cost effective answer that will work in what you already have (DimPro).
 
Alternatively, as suggested, SI bass is actually quite nice and again responds to normal bass processing like the real thing would. For simple stuff it can be quite nice with a little tweaking of the internal controls (and proper processing).
 
My old "go to" bass sound though when I was just starting out with Sonar was a specific patch in the Zeta+ banks. It's called "Picked Alembic" (caught my attention because of our ole pal bapu). I however own Zeta+2 which is a separate upgrade so I'm not sure if that patch comes with the basic Zeta banks in SPlat.
 
Again a nice sound that responds well but not quite as realistic as the EB5 or even SI VSTi's. But it cuts well and sounds good. Kind of modern style bass (which seems to get further and further away from the real thing even on rock... much to my chagrin).
 
The IK bass thingies are supposed to be quite nice as well but really I got what I need for bass sounds already with the tools I have.
 
Of course if you own something like Kontakt there'll be a mountain of useable stuff in there too.
 
Oh and check your account for the Brian Hardgroove pack for Rapture (if you had a membership when that was added as a freebie). It's an equally nice (and again created by Craig Anderton) sample pack using a Steinberger (much snappier/brighter/modern tone than the EB5). This one works in Rapture.
 
If you did NOT have a membership at the time then I think it's for sale in the Cake store and again will likely goes on sale from time to time.
 
My philosophy is always try to use the tools you have before hunting around for/dropping cash on/spending time learning something new until it becomes COMPLETELY clear those tools aren't up to the task. THEN go hunting around for new stuff.
 
I, of course, am a cheap/broke arsed SOB. lulz
 
Good luck and enjoy your new toy.

i like the Si bass for simple stuff, but I mostly use the NI Rickenbacker bass... many preset sounds give you a full range of sounds.  It's hard to get a bass to stand on its own out in a mix unless you do some careful frequency management, and maybe add another bass (synth) with some special qualities blended in. 

It often helps to put whatever bass you are using through an amp sim like TH3, Amplitube or Guitar Rig. There are other dedicated Bass amp sims out there. I usually use Amplitube and favour the Fender and Orange Bass amps.

I can't speak for the EB5 but I don't think the SI Bass is in the same league as the Scarbee/NI Rickenbacker, let alone Trillian.

Although the built in Sonar bass is good, I am a huge fan of the three Kontakt Scarbee basses (Jay Bass, P Bass, and Rick Bass)—each sold separately. (These are Fender Jazz Bass, Fender Precision Bass, and Rickenbacker 4003, respectively).
 
I could cut almost any rock, pop, or country track with just the Jay Bass, but I definitely use the others (probably 60% J, 30% P, and 10% Rick).  The Rick is a little dominating, but very cool.
 
You may not want to invest in all three, but they are definitely worth it and all come with a number of different presets.
 
Edit: In my percentages, I forgot to mention the EB5 which I have, like, and use, so that will skew the numbers a bit.  I just tend to gravitate towards the VIs I am most familiar with.

Sanderxpander
I can't speak for the EB5 but I don't think the SI Bass is in the same league as the Scarbee/NI Rickenbacker, let alone Trillian.

Likely not. I think folks are just saying it works well in a pinch and worth checking out (at least I was).
 
Edit: but as an owner of the DP EB5 I'd bet it would stack up quite nicely against third party bass synths/samplers.

I mostly record real bass using a customized Yamaha. For album recordings the sound can change from song to song, but for my backing tracks I need it to be the same from song to song. In the past this was simple with midi velocity set at 90 and using the same patch.
But now I'm faced with using Wave recordings and it becomes challenging especially with real bass. Over time I keep changing my pre amp, or I upgraded my Pups etc.
So I'm in the process of updating all my backing tracks to real bass, But in the mean time I have very good results using the SI Bass and the Jazz Bass patch. I tweaked it just a little EQ wise, but not much. I have trouble telling the difference sometimes when I listen..   "Did I play real bass or is that the SI?" The sound is very good for backing tracks,,   I can play a more interesting line on the real bass, I'm a bass player, not a keyboardist. but I'm fussy and I hate string squeaks and pops so certain lines come out tighter and cleaner when using midi.    I would never use the SI on an album but it certainly works for Backing tracks and quick demos.
I didn't like any of those Gibson basses,, But then I never liked Gibson Basses anyhow. I started life with an EBO short scale.. Boom Boom...
90% of the synth bass patches sound like a tuned fart to me. I'm talking the ones that try to be real bass. Synth bass is a whole other animal and is lots of fun on some songs like Mony Mony.

I play most of my bass on a Warwick 5 string Rockbass
 
Best results of all have been through blending a direct DI with the output of my Behringer Bass V-Amp

yes I should add, you can pick up a bass at a pawn shop for under 100 bucks. this is truly thee best route for a real sounding bass. that is if you can play one (that's not a dig either)

Beepster
 
 
My philosophy is always try to use the tools you have before hunting around for/dropping cash on/spending time learning something new until it becomes COMPLETELY clear those tools aren't up to the task. THEN go hunting around for new stuff.
 

I record my own bass, but I think this is good advice
What do you think is missing from the tools available?
All the best.