Senators are not experts on every topic that they govern over, so they solicit advice from experts.

...and In this case 2/3 of the experts called were/are competing for the government's business.

Edit: Strike that ... 1/3 of the experts is asking to compete for the government's business. 1/3 already have a monopoly for this work.

I'd say that's pretty "head to head".

As long as "head to head" includes interaction mediated by the Senator currently recognized and the chairman of the committee. In my opinion this mediation eviscerates any "direct conflict" between two people who are not senators.

Agreed. However the "experts" are not allowed to address each other individually. Senators ask a question to an expert and the expert addresses his or her answer to the Senator.