Hackman way too old, Triplehorn too reserved and upper-crust.
Hackman looked like a REALLY old geezer in the film. Not sure how old he was in 1993, but even with the wonders of make-up he looked about 70. Even thinking Triplehorn would consider kissing him, much less boinking him, is absurd and, well, creepy.
The problem is casting. The character played by Hackman should have been someone mid-way between the old partners and the young Cruise- probably a late 30's guy. THEN all the whoring and scuba diving would make sense, as well as Triplehorn's semi-attraction to him.
And Triplehorn is too cool and in-control for the role. In a marriage, she'd run the show and Cruise would be kept on a very tight leash.