I have had extensive experience with Sparkos op amps. These op amps are absolutely awesome, but it’s important to know that they do require a significant amount of voltage and current to sound good. It’s easy to starve these op amps and they will sound lackluster. They run in Class A (not as much as the Burson V4), but enough where you need to heatsink the regulators. You also need a significant amount of main power supply capacitance for the Sparkos. Not sure if this amp has that on the power supply. Since it’s only powering LM4562 op amps, it may have very little capacitance for the pre-driver circuit. The big caps may be only for the power output section.
BrownDog sells a vertical adapter for DIP8-to-SOIC,
http://cimarrontechnology.com/dip8toso8adapterpn031101b.aspx
but I don’t think you are going to have the space to place this. The LM4562 is a dual-channel SOIC (SMD) op amp and you have limited space. (maybe you can try to flip that main amp heatsink upsidedown (but I suspect it’s bolted to the case for heat transfer).
The very best non-discrete op amp I know is the AD797, but these are single channel and still require that vertical single-to-dual adapter above. If you wanted to try upgrading the op amp, the best I see is something like the AD8512-BRZ. It’s also a dual-channel SMD op amp and has decent noise/distortion/settling characteristics (not nearly as good as the AD797). Though, the default fallback is always the OPA2132.