I bought the Manley Chinook almost one year ago. I replaced all of the stock tubes with NOS Siemens Halske from Vintage Tube Services. The sound was much improved and I haven't had any issues with the device. I really like the unit a lot. I did contact Manley with the same question about input/output tubes in terms of overall importance and replacement priority. They helped me decipher the schematic so I knew which tubes were which and they offered guidance. In the end, I replaced all stock tubes at the same time, so it really wasn't an issue because the input/output tubes were replaced with matched pairs. Give Manley technical support a call and contact Andy at Vintage Tube Services regarding tube rolling ideas.