Easy Mike, nice to see you pushing the envelope!
You dont need to treat the 3rd deck as a bridging track, treat it as a track in its own right.
How I approach my 3 deck mixing is this:
Setup decent loops at the beginning of every track, Cue2 is my go to. Hammer that in time and let it roll. Now you can effectively leave this to do its own thing and bring it in when you feel comfotable.
I usually go for something melodic and in key, neuter the bass and take some off the top, but leave the mids. Bring it in with the linefader about 2/3rds up.
Take some off the two rolling tracks mids and highs to make room for number 3, bring it up slowly when nearing the drop/break.
A lot of dnb tends to have small 4 bar breaks where everything goes silent just before the drop. Use this to switch the bass to the incoming track.
On the drop, kill 1 outgoing track totally, kill the bass on the track thats still going, roll down the highs and take the line fader down a notch.
Now go grab a new tune for the deck youve just stopped. Rinse, repeat, double drop.
Theres a LOT to do in a small window of time aswell as making sure everything is tight! Never have 2 basslines going at the same time, it simply doesnt work with dnb.
Its also very difficult to do 3 decks with liquid dnb, theyre so sonically full already your gonna end up with clashing vocals and all sorts. All other sub genres tend to work nicely as only half the tracks have vocals.
Treat the eq like a cup of water.
1 track fills the cup 3/4 full. If you put another whole track in there your gonna get all wet. So take out some of the sound to make room for new sound.