PlayStation2 games with Dolby Digital sound only use it for cutscenes, while gameplay is 2-channel stereo matrix encoded in Dolby Surround or Dolby Pro Logic II. That means you can get surround in-game regardless of how you connect the PlayStation2. A handful of games support 4.0-channel DTS sound in-game, which requires using the optical output from the PlayStation2.
For games using Dolby Surround/Dolby Pro Logic II, remember to enable Dolby Pro Logic II Movie or Game mode (or the Dolby Surround Upmixer if your soundbar has Dolby Atmos support). Also check the in-game settings to enable surround. Some games that support Dolby Surround/Dolby Pro Logic II have no special setting for it and always output surround when the game is set to stereo. Games that support Dolby Digital in cutscenes or DTS in-game must always be manually set to output those.
The Ratchet & Clank games are pretty good in surround, enough to help you locate enemies.
Klonoa 2 is good as well, especially considering it’s a 2.5D game.
Burnout 2 and 3 also have nice surround.
Beware of Jak II however. It has the front-to-back axis reversed in its sound panner, so things happening in front of you are heard from behind and vice versa. Jak III and Jak X have correct directionality. The original Jak and Daxter does not have surround encoding, but while you don’t get directional sound, playing it through Dolby Pro Logic II or Dolby Surround Upmixer does open the soundstage a bit.