Probably not. Generally, in my opinion, I wouldn't expect to be able to significantly "improve" a well-designed integrated CDP by relegating it to transport duties and adding an off-board DAC. (I'm assuming that's what we're talking about?). Just too many new variables, and unless you're spending orders of magnitude more on the DAC than the CDP (and why do that), you could easily end up doing worse. So, under the circumstances, equal performance is likely not such a bad result. Not what you were after, I know, but maybe not all that surprising.
Now for what may be your central question -- then why bother? Personally, if your goal is to continue spinning CDs, I wouldn't. Full stop. But if you're looking, now or in the future, to convert your medium and your transport to something computer-based, then an off-board DAC is of course required (unless you've got a usable digital in on your CDP and can thus repurpose its DAC...). And in that case, if you find a combo that equals or betters your reference CDP, then you totally win. Conversion succeed! Or, at any rate, that's how I look at it.