Hey El, it's an analogue eg circuit, one of the most basic eq circuits is in your guitar(s), the tone pot shorts frequencies to ground via a capacitor (bit of a simple low pass filter (tops to ground)). So analogue eq circuits combine various components which do different things (caps (and their values) being one of them) to achieve the desired tone/frequency changes (boost/cut around a centre frequency (which I'm guessing is what Robs up to ?)). EQ has 3 basic variables, gain (boost/cut), centre Frequency (often called Q) and width/slope (how much either side of the centre Frq is affected (notch (very little) to shelf (very broad))). This is called parametric EQ (includes adjustment for all 3 parrameters), you can then have 3 or 4 band parametric EQs (like the better mixing consoles) thus 3 adjustments per band (band are divided usually into bass, low mid, hi mid and hi).
Your MP1 eq circuit has bass, mid, treb and pres, it has boost/cut for each but the centre frequency and width/slope of each band is set (by the values of various components and the circuit design). You could presumably get the similar results as Rob by setting your MP1 eq flat and using a decent parametric eq and dialing up the sounds...
That said, knowing what I do now, the MP1 eq could use some improvements, but IIUC, Rob made a selector to pick between a range of cap values for the same cap(s), a parametric does the same but has infinite values between its start/stop and a knob to select them. Not to cast any nastershams on Rob, he likes to fiddle