Hi Todor, and welcome to the forum.
My short answer: there are three areas that define the sound of a tape machine: the transport, the heads and the electronics. The transport has the largest influence of the three. The Studer A80 is one of the best transports. An A80 in good running condition is a joy. Studer heads are also excellent.
The Studer electronics are generally not to my taste, at least anything they made in the solid state era. The A80 was made in several versions over time. The transports were basically similar, and any version is good. They differed quite a bit in their electronics. Luckily you have the version that has the reputation for having the best sound.
I see nothing wrong with upgrading the passive components, meaning the capacitors and resistors, with better ones if you proceed slowly, confirm that you haven't changed the performance of the machine, and listen to be sure you like the direction the sonics are going. Don't assume that parts are better just because someone on the internet said so. I have been down that road, and found for instance that some parts that were "audiophile approved" contributed to an etched and dry presentation. If you are doing this to make it sound better, you must use your ears to confirm that you're going in the right direction.
I would leave the transistors alone. The general trend over time has been for transistors to get worse, not better. You might be able to improve upon them, but only if you have serious expertise in this field.
And the transformers, well I would only replace those if you are really sure that you have something better. Most of what's easily available will not improve on the performance of what you already have.
Good luck, and report back if you make progress.