There was a limited CD release of the original soundtrack back in 2000, which featured three versions (vocal, solo guitar, solo sax).
However, I have a feeling that the version you're after is one of the following two rerecordings of the theme:
1. Originally recorded for a CD titled "Charles Gerhardt Conducts the Film Music of Lee Holdridge", with the London Symphony Orchestra. As I recall, it begins with a solo piano statement of the theme and then swells into a full-blown orchestral arrangement.
The same recording is also available on a CD titled "Ron Howard: Passions & Achievements". You can hear a snippet of it
here (track 3).
You can purchase the Gerhardt CD at
Screen Archives.
2. Recorded by Erich Kunzel & the Cincinnati Pops Orchestra for a CD titled "Sailing". Telarc's page for the CD is
here, and a clip of it can be heard
here (track 5).
It's possible that both rerecordings come from the same arrangement, which may make telling them apart based on listening to the clips difficult.
For more information regarding some of the various releases featuring music from SPLASH, also check out
Soundtrack Collector.