Do Toslink Coaxial adapters work well or .......

Optical is the worst type of connection. Stay away from it.

I used one and still on one but I used it on a Sat reciever
that only had a Toslink. I really can't say that I noticed any difference good or bad. But a Sat receiver may not be the best acid test. I don't use it anymore since the recievers have coax since I prefer the coax over toslink.

Network Coaxial adapters offers you the ability to connect two BNC cables to one BNC cable.Some types of adapters are series adapters, coaxial,SMA adapters, SMA connectors and gain equalizers.

You can put a reclocking device like a Monarchy DIP, Theta TLC, or Genesis Digital Lens in between and it will convert the signal for you.

Alternatively, there are dedicated media converters out there that will convert between optical TOSLINK and coax SPDIF without any of the jitter reduction circuitry.

Out of curiosity, what are your DAC and source that you are so in love with them?

The MSB Digital Director is a good way to go. MSB no longer makes them, but one can be had on the used market for about $100.00.
My situation is a little different than yours where my transport is coax and the digital input on my Dspeaker Dual core 2.0 is optical. I use a high quality glass optical cable from Wire World and experience 0 issues.

Good luck