The proliferation of bandwidth-hungry multimedia traffic over IEEE 802.11-based WLANs has over-crowded the ISM bands. The opening of the UHF TV bands by the FCC for unlicensed opportunistic operation promises to relieve the demand on these bands. However, supporting bandwidth-intensive media streaming applications over TV white spaces can be quite challenging. This is due to the unpredictable nature of spectrum availability combined with the fluctuations of channel quality. The realization of this herculean feat through unlicensed usage, whilst providing protection to licensed primary users, requires intelligent and adaptive protocol design. In this paper, we propose a QoS-aware parallel sensing/probing architecture, called QASPA, which exploits inherent channel and user diversities exhibited by the wireless system. Aiming at maximizing sensing efficiency while achieving a high detection accuracy, QASPA incorporates an adaptive double-threshold-based sensing mechanism. It also embodies a cross-layer protocol, which uses an adaptive framing structure to minimize the control overhead, and a novel spectrum assignment strategy targeted at improving the spatial reuse of the network. The proposed spectrum assignment strategy supports both channel bonding and aggregation. Our simulations validate the ability of QASPA in guaranteeing the demands of high-bandwidth opportunistic media streams while supporting low-bandwidth streams. They also show the superior performance of QASPA compared to the scheme used in the ECMA-392 standard (for opportunistic indoor streaming).