The ICOM SP-23 (SPK-08) and Yaesu SP-8 (SPK-04) are intended to cosmetically match ICOM and Yaesu receivers and transceivers. Acoustically, their performance is nearly identical. They both work on any receiver with an external speaker jack, and have push-switch settings to reduce either high (treble) or low (bass) sound in order to reduce shrill interference or emphasize voice tone.     

     The VALOR VS-6 (SPK-07) is a compact, quality speaker for mobile applications; it has a treble-cut switch to help reduce impulse noise interference from car engines as well as annoying background hiss on a receiver or scanner. 

    The GAP "Hear It" DSP(SPK-05) is an active filter; that is, it isn't just capacitors and resistors, it has electronic components like ICs and transistors. It is used to cut off high and low frequencies much more accurately than simple tone controls. Therefore, I'd put it with the external speakers that have tone controls.