I know nothing about ISA Sound Blaster noise levels or how to modify them to get cleaner output, but as a headphone user I can say the output on Orpheus couldn't be any cleaner. I expect the same applies to MK8330 and Orpheus II too.

On my system I do get these odd low volume beeps during boot up that then fade out with Orpheus though, some games are prone to cause it too. I assume this is the motherboards doing, I bought it as recapped but I have no idea did the recapper do a good job or not. At least the solder joints look good and the system works fine otherwise.

A Sennheiser, cool! My father had one, a HD-424. The one with the yellow ear pads!
It was often seen in TV, too. Space 1999, for example, I recall.

Soundcards.. Don't forget analogue specs like signal-noise ratio (SNR) and channel separation.

When I got my Asus Xonar D1, I realized how thin old soundcards can sound.
The D1 had an SNR of 116 dB, a far cry from those 90 dB of the 80s/90s.

That being said, don't get me wrong.: These specs aren't useless with old source material!
The better specs were noticeable with emulators of all kinds. NES, DOSBox, C64 etc..
Also MOD and MIDI files..

Headphones.. In the past, eletrostatic headphones were top notch.
Companies like Stax made these excellent headphones. They require high voltage, however, so a special headphones amp is required..

Edit: The Pro Audio Spectrum 16 isn't all too shabby, sound wise.
Unfortunately, it doesn't support SB Pro modes. Just SB 1.5 emulation and OPL3, aside from PAS/PAS16 mode.

Alternatively, the Windows Sound System reference card (WSS) seems to be fine.
Or the AudioTrix Pro, or the EWS 64XL..
Anyway, there are likely more fine candidates out there.

Edit: Or get an SB32/AWE card and use digital output/Toslink?
A high quality S/PDIF receiver/amp could then do the conversion to analogue.

Shponglefan wrote on 2022-09-30, 02:01:

On a related note, what are some good strategies for quieting older, noisy cards?

Two basic suggestions concerning analog noise levels and general 16-bit soundcard inclusivity:

• Leverage the line output if available. Disable any onboard amplification where applicable.
• Take the time to appropriately configure the soundcard's onboard mixer for your specific setup and use cases. Many of the tips and techniques commonly used with full, external mixing consoles are likewise applicable here, and, at a minimum, should include some degree of level adjustment and the muting/disabling of unused channels.

For ISA the high class Terratec Cards have a very clean output just like the most Turtle Beach cards.

Some recommondations for soundcards with very clean analoge output (ISA Cards only):

• Terratec: Maestro 16/96 / Maestro 32/96 / EWS64 S/L/XL/XXL
• Turtle Beach: Tropez (Plus) / Malibu / Tahiti / Fiji
• Guillemot: Maxi Sound 64 / Maxi Studio
• Creative: AWE64 Gold
• Miro: Sound PCM 1 / 12 / 20

My top favorite is the Turtle Beach Tropez Plus with only two disadvantages: it lacks a WTH and is extreme rare.

The "OPTi 82C929A MAD16 Pro" sound card that was featured by Philscomputerlab a few years ago has a very clean output - plus there is a complete rewrite of the drivers available on github that improves compatibility with certain DOS games.

https://github.com/JKnipperts/OPTi82c929_Driver