This one seems to work like you asked:
$If($IsMatch($Left(<Sort Album>,1),"A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z"),<Sort Album>,
$If($IsMatch($Left(<Sort Album>,1),"1|2|3|4|5|6|7|8|9|0"),"zzz"<Sort Album>,"zzzzz"<Sort Album>))
You should still be able to type "zzz20" on the keyboard to jump to "20 Jazz Funk Greats", or you can of course adjust the amount of zzzs for all your ZZ Top needs.