Can the AriaMx be used for dsDNA quantitation

Yes, the Aria Mx can most definitely be used for dsDNA quantitation. In fact this is one of the most frequent uses of the instrument, involving both the Quantitative PCR DNA Binding Dye and Fluorescence probe experiment types.

Since it is a widely used technique, there isn't a specific application note dedicated to quantitation of dsDNA, but there is an extensive section on this experiment type in the qPCR Methods and Application Guide available at https://www.agilent.com/cs/library/brochures/Brochure_Guide%20to%20QPCR_IN70200C.pdf