Just a humble suggestion, but it would be helpful if you
were to list the tube complement in this product. It will probably get you the
desired input faster.
Also, if you key in VTL 2.5 in the Search Discussions box you’ll see there is already quite a bit of information regarding tube replacement feedback for this model.
Owning one a number of years ago, and if memory serves me (cautionary statement: I sometimes forget what I had for breakfast), I ended up with exceptional results using Mullard CV4024/12AT7 and Mullard CV4003/12AU7 tubes. The Mullard tubes are well balanced across the bandwidth and have exceptional midrange performance.