I understand from your complaint that you are hoping for audiophile quality sound from an average quality, 80's hybrid amplifier. I think you might expect better than what you describe but not greatly better. In 30 years, sound quality in discrete AB class amplifiers has moved on, leaving the many problems in those older, budget designs behind.
FWIW, changing Miller compensation caps (Ce7), doesn't have much to do with bass reproduction - that's the role of the feedback electrolytic, Ce5, which does seem a bit small in any case. The compensation of an amplifier is not something that can be independently tweaked to any significant degree without affecting stability margins, gain and bandwidth that require adjustments elsewhere. I don't think it will be disastrous to increase the value but I would start with a lower figure like 27-33pF. Check the type of cap already fitted - this is critical to compensation caps and it should never be a low cost ceramic cap unless it is of the NPO type (often indicated by a black painted top). Usually, audiophiles like to replace these with more expensive old parts like silvered mica and polystyrene caps but polypropylene fim caps are also fine. 'Careful with PS types - they melt with prolonged soldering time.
Finally, if you are hearing intermittent noise from the preamplifier, there are problems unsolved there. It is a complex, 3 band active filter using simplest possible transistor stages. It even looks noisy and something to bypass completely, but it also needs attention such as the replacement of all electrolytic caps. Service technicians are loath to do this without your acceptance because the cost of this is high, may not always bring about noticeable differences and shocks owners of old amps that have never been fully serviced in 30-40 years. Don't expect this to be done without negotiations.