Back in the 90's I installed with the Manhattan Center crew several Neve VR's, Our final room, the Scoring control room next to the 7th floor ballroom had a 96 frame VR which was only recently decommissioned. Anyway, the VR had a remote patchbay, and between that and the machine room runs etc. we designed large wireways under the floor, (no loose computer floor tiles here), including to the racks that held the monitor amplifiers in the front wall . This console already had all the panels perforated by Neve and we assumed that it would still run hot. Well, we had installed a couple of AC supply hoses to keep the amps cool and also the old CRT monitors above them, and surprise, the cool air was running through the wireways and being distributed underneath and being pulled up into the Neve. Of course we planned it that way all the along (not) but the console did keep reasonably cool and limited a lot of the heat related problems our other Neves were having, especially before the perforated panel process. So my recommendation would also be to increase cool air supply under the console.
Most IC replacement mods I have seen, or did, were pretty much failures, with the exception of replacing NJE4556 Jfets with more modern versions of the same IC family. Slightly lowering power requirement sometimes, but more to bring the noise floor down I think we used 4580's, by staying in the same family you avoid a lot of the oscillation and other anomalies you can get. TLO84's for TLO74's etc. you get the idea. If the circuit is DC coupled, or an EQ circuit you better be prepared for unexpected results. There are many IC's that have a plus/minus supply, but they all do not center at the same place between the rails. Also Jfets have extremely high input impedances and that can affect circuit design. Others like the NE5532 are good at pushing output loads, and can push more current on it's output. ( thus the greater supply current needed) Most applications don't take advantage of these however, so in a pinch any dual op amp with the same pinout can often be used as a replacement. But, it is not a good idea to change IC's from the original design, especially in high quality pieces like Neve VRs, that use several different families of OP amps for different reasons.
I couldn´t be happier with the desk, no GAS for any other big name desk over here.
But back in the 70s my personal test bench was a bunch of budget gear cobbled together. To extend my distortion resolution floor I fed the product output from my Heathkit distortion analyzer into the input of a second hand Spectrum Analyzer (Singer). I had to run my Heathkit down -10dB from its nominal zero to suppress distortion caused by the Heathkit audio path. Neither piece of bench equipment delivered a great resolution floor alone, but the two in series gave me a few ten dBs more resolution. I think I paid something like $700 for that old used Singer spectrum analyzer (30kHz bandwidth, 40 dB dynamic range) now we can just about do that with a free smart phone app.
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