The quality of the speaker amp will determine the sound quality you get from the setup, SRD-7 is great with excellent 2-channel system amp that is warm tilted... can bring better low end and dynamics to the sound compared to the STAX solid state drivers, but clarity, speed, and details are basically no different. If you already have a good high-end stereo amp it would be cheaper, but if not an SRM-323S would be significantly less than an SRD-7 + good entry level high-end quality 2-channel amp.
I'd go with a used SRM--323S or SRM-353X STAX driver unless you can find a good used warm leaning high end stereo amp for cheap or are willing to go with a new amp in the $1k+ range. The differences between the SRM-323S and my Mjolnir SRD-7 + NAD C 275BEE amp setup are noticeable, but not 'huge'...speed and clarity are no different, details minimally different. What you get with the NAD C275BEE is slightly improved low end extension with a more noticeable impact, better dynamics, and a fuller sound.