No @inna, I meant it is economically unwise to buy a Revox (and I'm assuming a Studer) that is in need of restoration rather than one that needs none. A good working condition example can probably be acquired for less than the price of a not-so-hot one with the cost to restore it added.
To your new point directly above, if the sound of your tape recorders electronics (used as a pre-amp) is better than your active pre-amp, it is time for a better active pre-amp! There is also the matter of the recorders output impedance (at all frequencies) and voltage, etc., very important in regard to driving the power amp.