I searched in my books and found the Tango Maria, Christian, it's numbered as SEM 13 in Volumen IV - 31 PIEZAS ORIGINALES PARA GUITARRA (3 inéditas), a SONETO (Madrid) publication edited by Melchior Rodríguez. It says there that you have to tune the 5th string to G and the 6th to D. I'm now digging into Sor's Opus 60, otherwise I would give it a try, it is so nice.
As for the other composition you mentioned, Preludio sobre un fragmento de Mendelssohn, I also found it, it's SEM 14 in Volumen III - 35 PRELUDIOS ORIGINALES PARA GUITARRA (4 inéditos), in the SONETO (Madrid) publication indicated above. It seems more complex than Tango Maria.
I assume, naturally, that the guitar is one of yours. Very beautiful and clear sound. Any particular model? Spruce, cedar, 650 mm, double top (nomex), raised fingerboard, what?
1972 - Kuniharu Nobe #8, 658/51, Spr, IN RW, Tokyo, JP
1979 - Ryoji Matsuoka No.40, 650/51, Ced, IN RW, JP
1987 - Aria A558, 650/51, Ced, lam RW, Nagoya, JP
2014 - Hermanos Camps Master Nº 3, 650/52, CA Ced, MG RW, Banyoles, ES