RMS values above 0 dbFS?
0 dBFS refers to a full-scale sine wave or more rarely a full-scale square wave.
ITU-T telephony Recs. P.381 and P.382 and reportedly the paywalled digital audio device measurement standards AES17-1998 and IEC 61606 define that full-scale sine wave is 0 dBFS. ITU-T Rec. P.10/G.100 (11/2017) does not make the distinction and defines dBfs (sic) as &quot;relative power level expressed in decibels, referred to the maximum possible digital level (full scale)&quot;.
Full scale DC has the same RMS value as a full-scale square wave, but is 3.010299956 dBFS RMS if the 0 dBFS reference is a full-scale sine wave. Looks like the different programs use a different reference (square or sine). Samplitude Pro X might use some approximation of RMS that gives in this case a 0.1 dB unit error.
The calculations:
$$\int_0^{2\pi}\frac{\sin(x)^2dx}{2\pi} = \frac{1}{2}$$
$$10\log_{10}\left(\frac{1}{2}\right) \approx -3.010299956$$