It looks to me as if the dialogue immediately preceding the speech is between Simmons and James Mason of Virginia.
and Senator Clingman is not complaining about the tariff, he is disputing Senator Simmons' claim that the new tariff will yield over $100 million in annual revenue
Which is a complaint about the tariff, or exactly what you said he was not doing. Senator Simmons maintains that since so little of the tariff is collected in southern ports that his estimates are correct. Senator Clingman says that the senator from Rhode Island is overlooking imports landed in Northern ports and destined to be shipped south, which he puts at $150 million per year. Since Senator Clingman provides no support for his claim it's impossible to take them seriously, any more than you can accept Senator Simmons' estimates.
You are free to dispute either senator's estimates all you like, but the point of the matter is their economic reasoning. As Clingman notes, exports don't magically happen for free. Something must be given in return for them, and if the south exported $220 million worth in goods, they had to get roughly that much somewhere as payment for those goods and the two sources are either monetary payment from abroad, or in the form of imports from abroad. The same would be true whether the export figures were $1 million or $500 million. As for what actually happened under the Morrill bill, trade with Europe died off almost entirely.
Regardless Senator Clingman is not threatening secession over the tariff
But he is saying that Lincoln will go to war over it.
he is not saying that secession was the reason why seven states seceded
But he is saying that Lincoln will go to war over it.
You are overlooking a third source, payments from domestic sources who then sold that cotton abroad. Which would allow the southern planter to spend his money domestically. Assuming, as you seem to be doing, that the planter spent all his money on imports leaves nothing to sustain the domestic economy with or to buy more slaves with.
But he is saying that Lincoln will go to war over it.
Which is nonsense since, as Senator Simmons pointed out, we're only talking about $3 million in revenue. That's less than 3% of the total revenue estimated by Senator Simmons. Nobody would go to war over a minor issue like that. President Lincoln must have been motivated by something else, like preserving the Union.