This is just my personal opinion. Solely on sound quality, separates only have the advantage if the speakers are a difficult load (big power or current requirement). Nowadays high quality integrateds costing up to $20k or more are capable of stellar performance, surpassing the quality of separates in the same price range. There are many great sounding integrateds in the $10k mark thereabouts.
My experience is only limited to integrateds costing up to $10k. The sound quality of the $9k integrated which I currently own actually surpassed the performance of the costlier separates costing up to $15k, which I also own.
In summary, in my book you need to spend considerably more to beat the performance of a good integrated amp. If the integrated costs $10k, you may need to spend 20k or more to beat it. A $10k separates will likely sound worse or inferior to a $10k integrated amp.