You are right, this is not my favorite question. I'm not known for commenting subtile sound difference. And the sound is not always in the iron ...
Some background why we started experimenting with different transformers for the OV560 mkII rev06:
The RÜP301 / RK204 can't be manufactured anymore, the original core material disappeared from the market. We asked Pikatron to design a follow up to the original specs - the RÜP118865 - but it was unclear how long it will take, and if we could afford the costs. At the end it didn't take as long as expected, and we decided to let them do a run of 50 pieces for us. However, the price of EUR 95,00 for an input transformer won't be everyones cup of tea.
In the meantime I did made two prototypes with the Haufe ST8456 and Lundahl LL1527 transformers and sent them to my beta tester. The ST8456 first measured its -3dB point at 18kHz, so I removed C4 which moved it to 58kHz. "For vocals I keep choosing the Haufe because of the open top end". We removed C4 for the Lundahl too but there was not much audible difference in the beta testers setup.
Long story short, the Pikatron RÜP118865 has the original sound, followed by the Lundahl LL1527. The Pikatron has the better measurement parameters, it is designed to the high German broadcast specs we had in the past.
The Haufe ST8456 is a cost effective alternative, with a slightly less vintage sound.
The output transformer in the OV560 is less critical, the original was also available without it. The RK310 from the original is still my favorite 1:1 line transformer, but my original stock dryed out. As far as I know Haufe can still manufacture it, but at a very expensive price.
The difference in price between the 3 models we now offer is not a mark of quality, it just reflects my inventory and the price I paid for it.
The Pikatron ÜP3288M and Haufe RK286/3 are used and taken from old broadcast modules. I bought the Pikatron RÜP1265 new in 2009 for another project that was never published.
Does this answer your question?