Noticed you are suggesting to load 1MGM.sf2.
This is a compacted 1MB soundfont with GM fonts only. This was the ROM preloaded in the AWE32 line of cards from Creative.
There are several, much more rich fonts available. 1MGM.sf2 has larger variants such as 4GMGSMT.SF2 or CT4MGM.SF2. These are copyright, but if you can get your hands on an old school AWE64 Gold installation CD you will find them there.
If your goal is to make EQ music "sound like it used to in 1999" then it depends on what you were hearing. Windows 98 defaulted to MS GS Wavetable Synth regardless of soundcard. You may want to search the web for a better version of the built in windows soundbank, gm.dls.
If your goal is to make the music not have issues such as skipping and clipping then you need another synthesizer. I wont recommend building a computer with ISA slots and getting a 20 year old AWE64 Gold. Software can fix these issues nicely.
In either event, I recommend OmniMIDI
https://github.com/KeppySoftware/OmniMIDI
This software allows you to load various soundbanks. It is a fork of BASSMIDI but is more updated and robust.
Once you have loaded the soundfont you can change the default midi device in Windows 10 by editing the registry under Computer\HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\M icrosoft\Windows NT\CurrentVersion\Drivers32 for 64 bit OS or Computer\HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Win dows NT\CurrentVersion\Drivers32 for 32 bit OS
There will be a REG_SZ key named "midi" which points to wdmaud.drv by default. This is the default windows audio driver which also contains Microsoft's software synth.
You should see your custom synth listed as "midi1" with the registered driver name.
Just copy the string from "midi1" and paste it into "midi"
To revert to default just make sure "midi" says "wdmaud.drv"