Audio Mirror Tubadour III tube rolling

Has anyone found a better tube than the 5977 subminiature tubes provided?

I need a bit more gain and by substituting a 6N1P, 6DJ8, ECC88, 6922 or 6H23P will double the DACS output.

I've tried both the EH 6922 as well the Voskhod 6N1P but they fall short sonically to the 5977. 

Thanks!