Excellent points by Kijanki, as usual. How did you calculate the 27 ns, though? If it were similar to a first order RC-type rolloff, for instance, the risetime and falltime corresponding to a 6 MHz bandwidth would be 0.35/6 MHz = 58 ns. Also, putting a bandwidth limitation corresponding to a 27 ns transition time in series with 25 ns I believe would result in risetimes and falltimes of about 37 ns, corresponding to the square root of the sum of the squares (I think :-)), which could very conceivably result in an audibly significant increase in jitter (timing fluctuations) with some DACs in some setups.
Another possibility to consider is shown here
, a (two-way) S/PDIF to AES/EBU converter that utilizes active circuitry, rather than (or perhaps in addition to) a transformer. It would not require an RCA-to-BNC adapter, and is described
as being suitable for applications up to 24-bits/96 kHz.
I have no experience with any of these devices, though, and no feel for the extent to which inserting the Hosa converter into the signal path might result in an increase in jitter (as a consequence of either its effects on signal risetimes and falltimes, or noise it may add to the signal, or impedance inaccuracy). Although the user comments that you will see posted at the B&H link by various pro audio people are generally very favorable, FWIW.
Another alternative, at considerably higher price points, would be certain "reclockers," whose purpose is to improve sound quality by reducing jitter in the digital signal. Some of them can accept S/PDIF inputs while providing AES/EBU outputs.
Apologies if my question is naive.
At this point in the thread it would seem to be well established that it is not :-)