Qsg is a great contact enhancer, but it is of no use on soldered connections.
Reference 3a is famous for their "minimal" approach to crossovers. My Dulcet mini-monitors have no cap at all on the mid/woofer. It is direct-coupled to the amp. I'm not sure how the crossovers are on the multiple-driver upper models. The tweeters on the Dulcet have one cap and one resistor and shunt. Very simple, time and phase correct.