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 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 Deaf Bonce M8-DSP offers a car with a factory touchscreen: its inputs and default channel plan, the software and what the manual leaves out, and how it compares with the Zapco HB 68 II.

How the Deaf Bonce M6C connects aftermarket amplifiers to a factory touchscreen: its six inputs and auto turn-on, wiring tips for Indian cars, and when the JL LoC-22 or M8-DSP makes more sense.

The Deaf Bonce MLA-4080 is the least expensive four-channel Deaf Bonce amp we sell: 80 W x 4 of Class AB with a high-level input. What Class AB means for size, heat and current, and what to pair it with.

The Hertz X 165 is the least expensive Hertz 6.5-inch speaker we sell, a coaxial built for factory replacement and head-unit power. Specs, when an amplifier helps, how it compares with the K 165 and DCX 165.3, and the scant owner feedback.

The Hertz X 690 is Uno's four-way 6x9 for cars with factory 6x9 openings. Specs, what the piezo super-tweeters really add, head-unit versus amplifier power, and how it compares with the Dieci DCX 690.3.

The Alpine DM-65 is rated at 92 dB, which on paper suits factory head units. Specs, M-Series hardware, the fitment figures Alpine leaves out, and how it compares with the SPJ-161C2 and S2-S65.

The Hertz K 165 is Uno's 6.5-inch component set, with its crossover hidden in the tweeter wiring. Specs, what that simple crossover trades away, head-unit versus amplifier power, and the little owner feedback there is.

The Hertz DCX 165.3 is Dieci's 6.5-inch coaxial for factory door openings: specs, how it runs on head-unit power, fitting it in Indian car doors, how it compares with the Uno X 165 and Cento CX 165, and what five UK buyers said.

The Alpine SPJ-161C2 is the least expensive Alpine speaker we sell: a shallow 6-inch coaxial for factory openings. What it offers on head-unit power, how it fits and when to spend more.

The Hertz DBA 201 packs an 8-inch driver, two passive radiators and a 220 W amplifier into one box for factory-system upgrades. Specs, what its 50-150 Hz range means, alternatives and sibling feedback.

Alpine's S-Series 6.5-inch coaxial examined: published specs and where Alpine's pages differ, head-unit vs amplifier power, fitment checks, how it compares with the R2-S65, S2-S65C and BRV-S65, and what US owners report.

Adding the Hertz DT 24.3 tweeters to factory door speakers: the specs, how the gentle 3.5 kHz filter behaves, where to mount them in an Indian car, and what the few owner reviews say.

Eight amplified channels, six high-level inputs, a 31-band EQ and app or PC tuning: what Alpine's PXE-R80-8 can run behind a factory head unit, where its limits are, and when the PXE-R100-8 is worth the extra.

Alpine's entry-level E-Series DSP amplifier takes a factory head unit's speaker outputs and adds a 15-band EQ, crossovers, time alignment and 4 x 25 W. Here's what it can drive, how it installs, and who it suits.

The Alpine HDS-990 is the Status range's hi-res media player, built to run alongside your existing head unit. Its formats and Bluetooth codecs, DSP and outputs, pairing with the HDP-D90, what it leaves out, its EISA award and what one owner says.

The Alpine UTX-M08S adds a high-resolution USB source, a basic DSP and a four-channel amplifier to a car without removing the factory head unit. Here's exactly what it connects to, where Alpine's documents disagree, and who it suits.

The Hertz CX 165 is the most affordable Cento speaker we sell: a sensitive, shallow 6.5-inch coaxial with an aimable tweeter. Specs, head-unit vs amplifier power, door installation and how it compares with the CPX 165 and CK 165.

Alpine's R2-S65 6.5-inch coaxial: official specs, head-unit vs amplifier use, how it stacks up against the cheaper S2-S65 and the R2-S65C component set, and what US owners report.