Thank you to Daniel M for helping me to put togther this formula:

=MID(MCONCAT(UNIQUEVALUES(IF(SUBTOTAL(3;OFFSET(E5: E1074;ROW(E5:E1074)-MIN(ROW(E5:E1074));;1));";"&E5:E1074;"")));2;8^8)

Which allows me to create a string based on how I have my auto-filtering. It
works fantastically.

I have now discovered that the MCONCAT formula appears to have a limitation
on the number of characters it can concatenate - I think it's around 50.

Thank you to JulieD http://www.hcts.net.au/tipsandtricks.htm for pointing
me in the direction of this UDF:

=CONCAT_RANGE(E5:E1074;";")

I would like to replace the MCONCAT function above with the CONCAT_RANGE
function. I've tried but can't seem to get it to work.

Thank you in advance.