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We investigate the low loss acoustic motion of superfluid ^4 He parametrically coupled to a very low loss, superconducting Nb ${\rm T}{{{\rm E}}_{011}}$ microwave resonator, forming a gram-scale, sideband resolved, optomechanical system. We demonstrate the detection of a series of acoustic modes with quality factors as high as $1.4\times {{10}^{7}}$ . At higher temperatures, the lowest dissipation modes are limited by an intrinsic three phonon process. Acoustic quality factors approaching 10 ^11 may be possible in isotopically purified samples at temperatures below 10 mK. A system of this type may be utilized to study macroscopic quantized motion and as a freqency tunable, ultra-sensitive sensor of extremely weak displacements and forces, such as continuous gravity wave sources.