Use DIY kit with exisitig integrated amp

1/  I have a Unison Reaserch Simply 2 SE tube amp. Can I use this DIY kit as the power amp?

2/ Also can I use it as my headpone amp?

skl

Do you mean the VT60? It can be used as power amp if your int. amp has pre-out

For headphone amp, need to do quite a lot of modification so I would suggest to build another one for headphone will be even better