So I tried using SampleTank 2 again. This time, I was able to make it work by setting it as a VST plugin. Whatever patch I define here is what will be save in the audio that I render (i.e., either M4A or AIFF). I need to run SampleTank 2 also at the same time so I can hear what it sounds like when I playback the song in BIAB.

I'm just wondering why was this mentioned in the video tutorial of PG Music? Is what I did just some sort of workaround?

I tried doing the same thing again, but this time using SampleTank 3 but BIAB did not accept it because it is a 64-bit plugin. I got frustrated again but after reading some topics in the site, I saw jBridgeM and gave it a try. Now, I consider my problem solved. But still, I'm thinking if defining the synth as a plugin a workaround or is that what it should be? I still haven't got a concrete answer from the support team. I hope there is a better solution.