I highly recommend you audition some different external clocks. I really believe you can improve on an internal clock if the external one is simply designed better. I changed my tune about clocking after hearing the results myself. Think about it this way, the external master clock can also be isolated from the noisy internal environment of the DAC; and power quality is absolutely critical to the performance of the clock. EMI & RFI can cause additional jitter in itself. The BNC cable also makes a noticeable difference in the sound. I know there's the adage of the clocking can't get better externally it can only get worse. This is old hat now. Any designer of their equipment isn't going to tell you they have a poorly performing clock. You have to find out yourself what else is out there. Black Lion Audio builds their clock internally straight into a modification of certain gear, including their own designs, and has compared the same clock externally in the same DAC. They measured the exact same amount of jitter on both configurations using an Audio Precision SYS-2722. I compared my Apogee Rosetta 200 running first as master with my digital interface slaved to it. I also compared my DAC slaved to the Big Ben and Black Lions's Microclock MK2. I much prefer the sound of the Black Lion clock. More 3D, better defined bass, lots of 2nd and 3rd order harmonics, very solid imaging, extended airy highs. The Antelope Trinity and 10M atomic clocks are also fantastic although pricey. The Black Lion is a steal and should cost 3 times as much. The Apogee Big Ben is solid. I haven't heard the Esoteric clocks or the dCS gear. Feel free to ask me anymore questions. I think you should dabble your toes in the external pool. You might find it eye opening.
