We mustn't confuse or obfuscate these two factors even though both determine whether a given amplifier will drive a give speaker satisfactorily.
Resistance, ohms, of a speaker is the main determinant of how hard it is for the amplifier to drive it without distortion. A statement that a speaker 'is' say 8 ohms is a subjective judgement of the lower ohm areas of its impedance curve plotted against frequency. A 4 ohm or less speaker will need an amplifier with a stiff power supply, not merely large but, more importantly, not weakening when asked to drive a low frequency at a low resistance. The amplifier's output in watts is not the most important issue here, although high power amplifiers tend to have big strong power supplies.
The dB measure of a speaker is how efficient it is - how much sound you get for each watt put in. 83db is very low. You need a lot of watts to drive it to high sound levels. Conversely a 100dB speaker is very efficient and a few watts will drive it very loudly.