This is why we have a forum search engine. Type in McCormack & you won't believe what comes back! Here below are a links to few threads that I found regarding SMC upgrades. Since you already have a deluxe (me too) it would only make sense to go to Rev A, since Rev B is already on par with the Deluxe models. The A+ level I believe only adds balancing transformers at the inputs; only a useful feature if you're using long balanced interconnects.
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1019175364&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&991233259&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1015172586&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&996515635&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?ymisc&1010515122&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1019175364&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&991233259&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1015172586&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?aamps&996515635&read&keyw&zzmccormack
http://forum.audiogon.com/cgi-bin/fr.pl?ymisc&1010515122&read&keyw&zzmccormack