Once a system of atoms is large enough that it's De Broglie wavelength is smaller than the Planck length. That system is now completely classical, and no quantum effects are relevant whatsoever. It is no longer a quantum object and should not be considered as such. An electron that moves really fast, or a lump of matter of sufficiently large mass, are not quantum at all, because their wavelength is too small.
Therefore, a clear delineation between quantum systems and classical systems is defined, and this whole question of "When does the quantum end and the classical begin??" is answered. There is no problem at all.
The experimental devices that are used to measure quantum effects are completely classical and not quantum whatsoever, so saying classical systems collapse the wavefunction is not ill defined whatsoever. This is a pseudo problem.