IMHO rarely does the SS equivalent of any tubed component, including DAC's, equal the latter in fluidity and, potentially, warmth. Warmth is however an additive usually depending on tube selection. Some tubed stuff is not warm at all. Usually, if you are fortunate enough to have very resolving speakers etc and are willing to pay the price you can find some SS components that can be both fluid and revealing, but rarely warmish in tone. To make the equasion more complex you must add into the mix the synergy between your DAC and transport, which as in the case of the Cal Alpha/Delta vs other transports is very important.
In your place, I would find a Delta to replace your transport before I would just buy a new DAC in your budget, especially if warmth of tone is a big priority. Actually, I would do neither, I would buy the Marantz I mentioned. I have its big brother in my system along with another tubed CDP and it is, in many respects, better than the tubed unit, and I easily live with it (but the tubed unit is still connected and is used for 'relaxed' listening sessions). Don't discount the value of having a transport matched by the manufacturer in the same unit. It can make a huge difference. The principle reason I believe for the current promotion of DAC's is the demand for something that can use other imputs by folks who no longer rely so much, if at all, on CD's for sources.
So while your Alpha can be improved in resolution etc, it is IMHO unlikely to be found in your budget range without some serious compromises you may not be able to accept.