It is same as any sane software volume control. Try the attached Javascript calculator with the numbers mentioned in ESS's pdf.
Type 30003 in the "sample to dBFS" field, click Convert and copy the signed value (-0.7657050592638563) dBFS.
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Minus that value by 10dB (-10.7657050592638563) and paste in the "dBFS to sample" field then click Convert. The result is 9487.781663803187.
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Javascript use 64-bit float (double) internally. To convert the value to 32-bit float (single) like ESS's pdf, click the "Convert to single" button and get 9487.7813.
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ESS's pdf said -10dB(FS) is 0.3162, type -10 in the dBV field and click Convert. 0.31622776601683794 is that value in double precision. The formula of dBV to Vrms (+/-V in the calculator) is same as dBFS to float.
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The only thing to concern is the input of DACs are not necessarily able to accept float input even if they can do floating point math internally. Which means float values beyond +/-1.0 leaving the playback software will be clipped by the ASIO or WASAPI exclusive API or compressed by Windows' CAudioLimiter when using DirectSound before entering the DAC. This phenomenon can be examined by my test files posted in #6.