If you only want to experiment, o.k., but otherwise it is an absurd use of the WA12. You use a mic-preamp with a Hi-Z-input as a DI. The job of a DI is to transform a Hi-Z signal to mic-level. This is exactly what the WA12 is doing, but it is doing even more: 'cause it is a mic preamp it transforms the mic-level signal to line level.
The Avalon is a bit special, 'cause it is doing exactly the same: it offers not just mic-level as most DIs, but line level too. So both of your units are doing exactly the same. Only the WA12 has - as a mic preamp - no mic-level output. And the Avalon - as a DI - has no line level input.
Only line-level comes out of the XLR-out of the WA12. To put this line level signal into another DI into an input that expects a pure guitar or bass signal (Hi-Z) doesn't make any sense.
If you want to use the sound of the Avalon + the TB12 in your chain, it goes like this: bass into Avalon. Then the mic-level output of the Avalon into the mic-in of the TB12. Or the line-level output of the Avalon into the TRS-input on the front of the TB-12 that is switched to line (simply press the line button on the right of the Hi-Z button on the frontplate.) The Avalon should always be first in the chain, 'cause it simply doesn't have a line input, but all of the outputs of the TB12 are line level. I only own the TB12, not the Avalon. If I understand the through TSR output on the front correctly this gives Hi-Z level output, so if this is the case you could although use the Hi-Z input of the TB12 if you're using the through output on the Avalon.
Why did you buy the TB12? You don't seem to have the basic knowledge what a mic-preamp or / and a DI are doing?
If you don't have a second use for the WA12 - using it as a mic-preamp for vocals for example - you kind of own two rather expensive tools that do the same in a different way. Might have made more sense to - for example - buy the WA76 from Warm Audio. Just saying...
