Is it possible to create a 2-line album title, basically a headline then subhead on the next line?

You can use html markup in the title field to do that (depending on the allowed tags on the option of the same name).

I tried adding br => () to the "allowed tags" field under Options > General but it didn't work to add a line break. Am I adding it incorrectly?

Hi.
Why don't you display the album title and its description using their dedicated fields (or another one if you use it for something else) ?
Then you just have to paste that in your theme :
< br / >

Good idea, the custom field could also be used as a sub headline. Of couse the function needs to be added to the theme files.

Thanks, I'm using the album description, so I could try the custom field for a subhead. Could I include it in the title tag? Now the title tag code reads this (in part):

Could I use this instead (not sure the code for the custom field, which I assume is "Custom Data" on the Edit Album page:

http://www.zenphoto.org/documentation/functions/_template-functions.php.html#functionprintAlbumCustomData
http://www.zenphoto.org/documentation/functions/_template-functions.php.html#functionprintImageCustomData

Thanks for that link. I'll see if I can get it to work.