Opamp Upgrades for Mixing Board

[WeAreAs1 at aol.com]

Hello listfolk,

I have a Yamaha RM2408 recording mixing board that was made in the 
mid-1980's.  It was pretty nice for its time, but I'm thinking that it's 
probably possible to make some sonic improvements to it.  I'm considering 
replacing all the 4558 opamps in it with more modern, better sounding parts.  
I'm also going to try replacing the carbon composition resistors in the audio 
path with metal film types (I'll try it on one channel first, to see how much 
effect it has on the sound).

Anyway, I'd like to get some suggestions as to what opamps to try.  The mixer 
has 24 channels, and each channel has four 4558's in it.  Each channel's 
audio passes through a total of seven opamp stages:  First, a unity gain 
differential follower (following the mic preamp's differential transistor 
pair), then four stages for the EQ section, one stage for an active low-cut 
filter section, and finally one last stage which buffers the output of the 
channel fader (and adds 10dB of gain) before the feeding the signal to the 
panpot and main busses.  The opamps run from a very clean +/- 16 volt supply.

I'd like to know what you guys think of the following types, and what you 
like or don't like about them.  I'd also like to hear of any other types that 
you think are worth checking out, and why.  I would especially like to hear 
from people who have actually done some hands-on comparisons, as opposed to 
just reading about specs.  

I'm probably not willing to buy a bunch of ten dollar Burr-Brown 
instrumentation amps (remember, I have to buy 96 of them for the whole board, 
not counting the handful of buss summing amps and aux busses), so try to keep 
your suggestions on the practical side.  I'll buy a few of each of the most 
likely candidates, try them out on a channel or two, then report back with my 
findings.

Here are some that I'm considering:

OP275
TLO72  (the old standby..)
NE5532  (very popular in the 80's... now??)
TLE2072  (ti's "Excalibur" series) 
NJM4560  (used in all Mackie products)

These parts range in price from about $0.35 each to about $2.00 each, which 
works for my budget.  I would consider buying more expensive parts, if they 
can show considerable sonic improvement (for instance, if even my girlfriend 
can hear the difference...)  I'd also consider mixing types - for example, 
using one type for the mic pre section and another type for the EQ stages, 
etc.

I know this subject is almost a religious debate for some, so play nice, 
folks.

Michael Bacich