There is also a Garritan forum at https://makemusic.zendesk.com/hc/en-us/community/topics/200575788-Garritan-General-Discussion?sort_by=recent_activity if you want to go there.

If you are using Garritan already, then you are presumably already using some version of the Aria Player to play them. Garritan sounds (a subset of their full packages) and the Aria Player come free with full Finale (MakeMusic's notation program) but I'm not sure the Aria Player is a solution to how strings sound (although I admit the GPO4 strings sound better to me that the GPO5 strings Finale loads be default). GPO is a package of orchestral sounds. You can see what they are at https://www.garritan.com/products/ .

Depending whether it is compatible with your computer's OS, you can probably upgrade your current copy of the Aria Player from the Settings tab.

If you type in "ARIA" into the search file on the page you linked to, then ARIA Player 1.959 is top of the list of results. 

However, note that the Player and the Engine are two different things. The Player update should also update the Engine. But if not, the Engine can be downloaded here:

http://ariaengine.com/support/aria-engine-update/

>The Player update should also update the Engine…<

Yep, sometimes it doesn’t. I’ve played Aria roulette a few times over the years trying to get the right versions of the player and engine to match the versions of Finale and the OS — but I’ve always been able to get things to work. Can’t say that it’s been an issue for me since Finale 2014.5, though. 

I don’t see how the versions of Aria can affect the quality of the playback audio.

Dear Everyone.

Just wanted to say THANKS and HAPPY CHRISTMAS for all the help you've given me - I'm downloading what's hopefully the right thing right now!

Thanks again for all your much-appreciated help.

Yours with much respect,

Chris.  Who's a proud user of Quick Score Elite Level 2, in my opinion the best notation software out there.