I think that there may be a slight language difficulty here. I know that you can use a reference clock with a Scarlatti clock. What I said was that you cannot use a Scarlatti clock with a Vivaldi clock.
You have to use a Vivaldi clock with the Rossini Player if you want to use a reference clock as the Rossini clock does not have a reference input.
The DAC ultimately defines the basic sound, not an accessory like a reference clock. So using a Vivaldi clock into a Rossini player would be a little better than using the Rossini clock. Adding a reference clock will make another small improvement. But it would not be as good as a Vivaldi DAC of course, irrespective of any clocking considerations.
I now appreciate that as you only play CD you would indeed need a transport if you bought a Vivaldi DAC instead of your Rossini Player. You could, like me, happily use the Rossini Transport with the Vivaldi DAC rather than the very costly Vivaldi one however, though as CD is your sole source the Vivaldi Transport may be a better choice ( silver disc is not my main medium for music). I understand your reservations having regard to the costs involved.
My real concern with your idea is value for money. I’m in the UK where the Rossini Player costs 21K gbp. The Vivaldi clock costs 12K gbp and the Rossini Clock 5.5K gbp. Cybershaft clock op21 is around 6K gbp by the time import and tax costs have been paid I understand. So you are looking at a cost difference between a Rossini Player/Clock combination and a Rossini Player/Vivaldi Clock / Cybershaft of around 12.5K gbp for a very small improvement, not inconsiderable, but small. To me the additional cost is out of proportion to the gain it will bring. Adding a reference clock IMO can only make sense in a complete Vivaldi setup and that is, no doubt, why dCS did not think it worthwhile putting a reference input on the Rossini clock.
However if that’s what you want to do then it is your money after all .