I held off switching to Squarespace 6 because of its lack of support for javascript-based syntax highlighters that I have used in Squarespace 5. I finally found a solution that may not be ideal but works. I am using Textmate 2 on the OS X that provides very nice syntax highlighting for most languages. Use the menu Bundels -> Textmate -> Create HTML from Document. Enter the HTML into a code block in Squarespace 6 and you have nice looking code. There is also the option of including line numbers.
Neat idea, thanks for the tip. I’m trying to get syntax highlighting working using
http://alexgorbatchev.com/SyntaxHighlighter/manual/installation.html
and
http://www.stevedigital.com/blog/2013/12/27/formatted-code-and-syntax-in-squarespace-6
This has been working for me in SquareSpace 6 and 7:
http://www.mikeraynham.co.uk/blog/2014/10/18/a8uiyyc3lopttbq2xa9es1ah0hthpq