What the Resolut M25-IN does, what MOST 25 integration means, which Resolut processors take it, what Resolut doesn't publish, and the analogue alternatives for factory systems.

What the Resolut BT-IN Bluetooth module offers, why aptX Lossless depends on your phone, what Resolut doesn't publish, and cheaper ways to add Bluetooth to a Resolut processor.

What the Resolut USB-IN HQ module does, which processors take it, what Resolut does and doesn't publish about formats, the cables you'll need and the alternatives.

What the Resolut A-IN module does, which Resolut processors need it, line versus speaker-level wiring, features Resolut lists as in development, and cheaper ways to connect a factory head unit.

What the Resolut SRC remote does, which Resolut processors it works with, the cheaper potentiometer alternative from Resolut's manuals, and who actually needs one.

Alpine lists the KTX-CSP1 measurement microphone kit for its OPTIM8 and OPTIM6 processors. Here's what it does, where it fits in OPTIM8 tuning, what OPTIM owners report about the processor, and who should skip it.

Which JL Audio products the DRC-205 wired remote works with, when you actually need one, how it compares with the VXi-BTC, and what it costs in India.

What JL Audio's five-microphone MAX kit actually measures, where it fits in DSP tuning for Indian cars, what installers and forum members say, and who should buy one.

Zapco's DAC Kit A brings the ESS ES9038PRO to the HDSP-Z16 V. We separate the published figures from the marketing, explain the likely kit count for each processor, and say who should consider it.

Zapco's DAC Kit B swaps the HDSP-Z16 V's output converter for an AK4490. Here's what that changes, why Zapco's figures differ between pages, and who should consider it.

What Zapco's ADC Kit B changes inside an HDSP-Z16 V processor, which inputs it affects, what Zapco hasn't published, and whether it's worth asking us for one.

The JL Audio VXi-HUB joins several VXi DSP amplifiers into one network for tuning, presets and remote control. We cover its ports, the six-versus-five amplifier question, optical audio distribution and whether your system needs one.

The JL Audio VXi-BTC links a phone to JL's VXi DSP amplifiers over Bluetooth for tuning and control, not music. We explain what it works with, how it compares with the DRC-205 remote and whether you need one.

What Zapco's HB DSP II-R remote controls, which HB II processors it works with (and which it doesn't), and whether it's worth adding instead of relying on the phone app.