okay... i did it... it took most of my afternoon, and then i had to go do laundry. sometimes i wish i was a Torian. they don't wear clothes.
no, scratch that. i never wish i was a Torian.
and now presenting....

that was the max i was able to achive. i cheated very thoroughly, so this in no way represents something you could do in a real game... at least, not this quickly.
the figure comes from the 11 terran freighters and 12 of mine. IF i had remembered to give the terrans another +1 route, you could multiply this value bu 24/23 to get an estimate for a max value (48,192).
my frieghers all occupied the same square in a big stack, while the terrans' were more spaced out (1 or 2 per parsec, most in a clump one after the other, but with a few stragglers). that explains the sine waves you see in the econ graph farther down (which could be offset by spacing out the arrival time of freighters).
this is how:


i played as the Korx and used the cheat mode to set this up. made the terrans my allies. for us both, i picked +30% trade and the merchantile party. i should have also given the terrans +1 trade routes, but c'est la vie.
on turn 1, i cheat built 208 SBs decked out fully with trade modules; force researched xeno ethics and neutral shipping, and cheat-built 12 freighters which i kept parked next to my homeworld.
next turn, i made contact with the terrans. they were too busy to talk to me for another two months. so i hit enter furiously. as soon as i could, i gifted them 208 SBs, 12 freighters, and all the trade techs plus xeno ethics. then i build 208 more SBs and 12 more freighters; those frighters were immediately teleported to the terran world, and trade was established.
it took them a while to get all the freighters to me. why is beyond me, but that's the AI for you (set on tough).
this SB array resulted in most parsecs being covered by 20-24 SBs (except 1 in 15 squares had only 8 SBs' coverage). about 2/3 of my frighters' way to the terran world, a thought occured. i allied with them (disabled all but conquest) and forced UP meetings until the allies-share-SBs agenda item came up (and it only took 2 tries!). that doubled the effect of every SB.
i didn't even bother taxing my 19 billion people. here's what my trade history looked like.

i also wrote down my income on the first of every game year (or thereabouts, sometimes i forgot).
game date (d/m/y): trade income1/3/26: 256 (first week of trading)
1/1/27: 3617
1/1/28: 12526
22/1/29: 18273
1/1/30: 21522
1/1/31: 31047 (alliance was formed during previous year)
15/1/32: 43817
toward the end, my trade revenue was typically 35-45K, but dipped down to around 18K at its lowest point in the 15-turn cycle.
also toward the end, the highest per-freighter value i observed was 2233/turn. i constructed the first set of SBs without any extra logistics points (Korx base ability: 6); it cost 27,918 BC. i constructed the second round with all the logistics techs and the hyperion log. system; it cost 12,771 BC.
so... constructing this thing in a real game would be unrealistic (unless you've already won virtually). but i think you could apply the principal quite well to a relatively short trade route; it wouldn't take too many bases, and it'd be much easier to defend. most of the income here is bonus anyway, so while i'm sure that goes up on longer trade routes... it goes up more if you can saturate them with SBs. you won't max out trade with a short route, but you'll still rake in bucks. also, get an econ treaty with whomever you trade, and you get a bonus 10%.
you could also use the principal of gifting SBs to allies, under the allies-share-SB UP law, to radically increase the industrial bonuses you can get from SBs on a manufacturing or research world. build 16, gift to an ally; build 16 more, gift to another ally, etc.
so... any questions?