Maximize the value of Voice over IP communications with Plantronics® DA Series USB-to-Headset DA60 Adapter. QuickDisconnect at the other end of the cord connects to any Plantronics Call Center headset (H-series). The DA60 adapter enables VoIP softphone users to conduct crisp, cost-effective client interactions. The DA60 is infused with digital signal processing for optimal call clarity, and SoundGuard® Plus™ protects listeners from strident transmissions, and an echo suppression feature facilitates natural dialog flow. Our sophisticated DA60 adapter includes PerSono Pro™ software, which equalizes softphone audio settings and displays transmit and receive volumes for every call. A tiered range of adapter solutions fits the budget and business requirements of every softphone-based organization. Retail Price $150.00

Key Features:

• Digital clarity, Plantronics comfort
• Enhanced VoIP sound quality
• Remote supervisor control for consistent quality

For more details see Plantronics DA60 datasheet

So what's the difference between the various Plantronics adapters?:  DA40, DA45, DA55 & DA60:
Plantronics DA40 is an affordable option that does NOT include the PerSono Software & does NOT have the inline volume & mute controls, but does support "Wideband" audio. Only works with the Plantronics H Series Headsets.
Plantronics DA45 is similar to the DA40, but has inline Volume/ Mute controls, Call Answer/End, supports "Wideband" audio & "Echo" management, & comes with the PerSono Call Software program. Only works with the Plantronics H Series Headsets.
Plantronics DA55 Does NOT include the PerSono Software & does NOT have the inline volume & mute controls, but supports DSP (Digital Signal processing) & Echo-Cancellation. Works with both the Plantronics H Series & Polaris Series Headsets.
Plantronics DA60 is similar to the DA55 but does have the inline Volume & Mute controls, comes with the PerSono PRO Software program & supports DSP (Digital Signal processing) & Echo-Cancellation. Works with both the Plantronics H Series & Polaris Series Headsets.