How are we wiring our Mono systems?

Our?

Count me out.

More suitable for "one ears" like Brian Wilson.

According to an article on Pitchfork, Brian Wilson, the co-founder of the Beach Boys, is known to prefer mono sound over stereo¹. The same article also mentions that the mono version of the album “Pet Sounds” was overseen by Brian Wilson himself².

Additionally, AllMusic reports that the 2004 reissue of “The Smile Sessions” was not in stereo, even though roughly 80% of the tracks were available that way³.

lewm,

I believe the dealer had it between the linestage and the amplifier.  He had a very young tech who built the comparator box and would also make the mono adapters for customers (put them in various vintage component cases with RCA jacks).  I don't recall what specific transformers were used, but some were current production and others were vintage; the most expensive being Western Electric transformers.   Based on recommendations he found on the internet, he built one such mono adaptors using two transformers (both Western Electric transformers) and that was the best sounding, but a bit pricey. 

I have no idea why transformers with zero gain sound better than a Y connector, although I sort of have a theory.  I suspect that the transformers introduce some phase shifting that actually improves the sound.  

The impedances (input and output) seen by the two devices would be very different in transformer connected mode vs Y connector mode.  That also would affect SQ of course.  I am actually trying to figure out how you would do it with transformers interposed between linestage and amplifier.  When you say "zero gain", I presume you mean 1:1 turns ratio, so the transformer is in essence isolating one device from the other. One problem with using an external Y connector, either between linestage and amplifier or as is done more commonly, between the stereo leads from a tonearm into a single pair of inputs on a phono stage, is just that, impedance gets messed up, because the driven device sees the output Zs of the two driving devices in parallel.  And in the latter case, each channel of the cartridge sees the internal R of the other channel (in the cartridge) in parallel with the input Z of the phono stage.  A good linestage with a mono switch incorporates resistors to mitigate that issue, in mono mode.

You know a lot more than I do about this stuff; I just sat there and listened while someone flipped the switch on the comparator box.  There were two transformers that were very good and quite close in sound--one was the somewhat expensive Western Electric transformer, the other a much cheaper modern transformer--which made the cheaper transformer a "bargain."  I am not a mono system person myself, but I do see how it is more practical in certain situations where someone cannot sit in the ideal spot for stereo listening but wants good sound.  One of the buyers of the conversion box has a crazy nice mono setup built into his kitchen where a lot of time is spent.  He has a three way system with a field coil woofer, a Western Electric 713b midrange compression driver (my personal favorite compression midrange driver), Western Electric 32a horn, and an RP302 tweeter.