Because space is limited in most S-10/S-15 applications, signal processor installations are usually limited to half-DIN models, which can be installed in-dash along with a single-DIN receiver using the appropriate installation kit. Even though it's been around for a while, Kenwood's KGC-6042A (MSRP $250) is a great way to expand your system's capabilities while filling up the gap in the dash. This dual-illumination unit combines nine bands of graphic equalization combined with two variable parametic bands. It also features a built-in active crossover with high-pass outputs for front and rear amplifiers in addition to a subwoofer output with as much as 10 dB of gain with crossover points that can be adjusted from 30 to 150 Hz.
When selecting an amplifier, the space issue will often come into play. There are two approaches that you must consider: choosing multiple small amplifiers, using space available under the seats, or going with a larger multichannel system amplifier mounted behind the front seat (in standard and extended cab models). If you're just looking to add a subwoofer to an existing high-powered aftermarket head unit, you can often take advantage of subwoofer controls built into many units; in fact, most head units priced more than $250 typically offer this capability. A great by-product of going this route is that the amplifiers built into these head units, when not trying to drive low frequencies, will sound cleaner and play louder through your full-range speakers. As most head units feature 15 watts or more of clean output, in a small cab, this is often enough to generate very satisfying listening levels. Obviously, if you want to have your system heard two blocks away, more power will be required.
If you want to go the route of a small, single one- or two-channel amplifier, either to drive a set of full-range speakers or in a bridged mode to drive a subwoofer, one of the most popular choices is Kicker's KX150.2 amplifier (MSRP $180). With its onboard variable crossover, you can adjust the KX150.2 for different applications, from driving full-range or component speakers, or a dedicated subwoofer. Bass boost is adjustable as high as 18 dB at a preset frequency of 40 Hz, which will give your system that low-frequency impact that will make it stand out from lower-powered systems. The KX150.2 includes both speaker- and pre-amp-level inputs. This insures that the amp can be hooked up to both factory-installed and aftermarket head units. Its small footprint (10.2x12.75 inches) and low height (2.5 inches) ensure that it will fit in tight spaces, such as under the seat of your S-10 or S-15.
If you'd prefer a dedicated mono amplifier to drive your subwoofer (bridging a two-channel amplifier typically adds small amounts of distortion and can't typically drive into 1-ohm loads), then consider the MTX Thunder 311D (MSRP $230), a dedicated mono amplifier, designed specifically to drive low-impedance, low-efficiency subwoofers. Into a 4-ohm load this little powerhouse delivers 155 watts RMS. Cut the impedance to 2 ohms and output rises to 310 watts, enough to drive any subwoofer likely to fit inside your cab. The built-in low-pass filter, set at 85 Hz with an 18 dB-per-octave slope, can even eliminate the need for a separate crossover or signal processor. MTX's Thunder EQ bass boost adds 6 or 12 dB of boost at 40 Hz. SmartEngage, which turns on the amp when it receives a signal input, makes it a great choice for factory upgrades. Its small size, 8.2x2.25x9.75 inches, makes it a snap to install.