I own three Monarch 4 strings - all of them are top of the worldclass ! I use to own about 20 basses in parallel and actually I play a Monarch nearly 80% of all gigs.
The YinYang for itself is a miracle, it's pure fun to take it and jam with it no matter how long... but I feel I don't need 3 Monarch 4s and this has the best condition of all and seems to reach the highest resale value I think - due to its exceptional construction and craftsmenship. There is absolutely no issue with this bass. If it won't go - I won't cry...
Compared to the Mahogany/Buckeye Burl VW Classic the YY supports slightly more the high-mid accents which is fine for tapping and fusion lines. The alder body adds the warmths on the lower register. Compared to the walnut Bolt-On Monarch the YY provides a more elaborated tone. The BO is a funk machine. The YY sits perfect in any mix - but that is true for all of the Monarchs. This particular bass is set-up with LOOOWW action and is very inspirating. The Monarch neck feels slightly beefier, yet smaller than the Emperor or Imperial necks.
Can't say it better than with the word of another well known TBer: The Monarchs are the aggressive beasts, the Emperors and Imperials are sophisticated cats. I'm really digging on the Monarch sound and design and sold my 2 Emperors long ago.