John, here was my answer to a similar question that was asked:

"Bass and guitar are written an octave higher than they sound. For example a true concert middle C, on a piano it is on the first ledger line below the treble staff C, is on the third space of the treble staff for a guitarist, i.e. written an octave higher than it sounds.

So if your MIDI bass line is for it's actual notes (concert middle C) and your sound source is expecting an octave higher bass line (written) you may loose the lower notes. Sometimes it is visa-versa. Every sound source and MIDI base line is either one way of the other and it's up to you to match them. But all you have to do is to transpose the bass line either up or down an octave so it matches your sound source.

For the in-depth Midiots I know there is some controversy over what is middle C. I am using the most common C5 MIDI note 60, read here:

http://www.electronics.dit.ie/staff/tscarff/Music_technology/midi/midi_note_numbers_for_octaves.htm

https://en.wikipedia.org/wiki/C_%28musical_note%29

I hope this helps and is not too confusing."

Now the question that I have is which low A are you looking to add? Is it a realistic low A that any 4 or 5 string bass can play? If yes that the above comments come into play and you would have to raise the BiaB bass track one octave. If it isn't then you would need to find a bass sound that covers the entire piano range of notes. There are some out there so google/bing can help you search for one.

I hope this helps.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware