Boutique amp is High Quality amp with high quality component, usually very expensive output transformer (200$ and more), usually use NOS tubes which can be very very expensive and they build after many years study.If you change position of elements or tubes or transformer or input you change characteristic of amp.Beacuse each elements(caps,resistor...) should have exactly one position and this is many years experience.And Boutique amps are usually built from less component as possible, only the necessary one.
It is not necessary they are PTP built.PTP is for small production.
For example:
Hughes and Kettner PURETONE have one knob GROWL which at maximum bypassing complete tone control for pure guitar signal.
Boutique amp usually sound fantastic and they are very dynamic.But for people who do not playing dynamic it is waste of money, beacuse you can sound the same from many less expesive amps.If you buy boutique amps you should learn to play guitar again to using, what your amp offer to you.
Zoran