Producer & recording/mixing engineer Joe Barresi (QOTSA, Tool, Soundgarden) gets down and dirty with that low end when mixing four different bass guitar tracks (DI and amps) to one big fat bass tone.
When dealing with several tracks, relative phase is an issue to consider and pay attention to first. Taking the time to do that might save you much time and effort when trying to dial in the perfect bass tone. It can really make or break a mix.
"Dead notes" (where the tone just suddenly disappears) are another teeth-grinding-hair-pulling issue you might have come across when mixing bass guitar. Joe usually likes Renaissance Bass or MaxxBass to help him deal with that one.
Depending on the character of what your mixing, LoAir might be a better fit to provide the low-end support your track needs. You can go from big, to "bigger" to gargantuan!
Last but not least is controlling your bass' dynamics in a way that contributes to the tone you're looking for. Joe achieves that quite easily with the CLA-76 Compressor/Limiter. Other options to consider are the CLA-2A and the CLA-3A compressors.
This video is part of a series of instructional videos with Joe Barresi. More videos in the series:
Also check out Joe's ProSound Workshop.
Music: “Mercury Gift” by Zico Chain