I don't know much about that amp but I don't think you can use pentodes in it. OCL means output capacitorless?
I bought my LDMKIV almost new from a person who bought MK6 since he wanted a balanced amp just because
He then told me that he would not afford to get other tubes for it. But he didn't regret his move from start.
I should also say that I had to get an external power supply for the heaters to use 6080/6BX7/CV4079 with special adapters in LDMKIV. You won't need that in MK6.
I got these from
@Deyan too. And plenty more adapters that aren't shown here. The external PSU is in the grey box and the adapters with cables to use it to the left of it.