A new Ultrasound came on the market: it was based no longer on the technology of the old GF1 but used the AMD InterWave DSP, which was co-developed by AMD and Gravis, and can be seen as its successor. 195 instruments, which covered more than what General Midi required, were on the ROM of the card.
For the purpose of compatibility it was switchable to GF1-mode via software, however with an obstacle, that is not farther tragic on the second glance. There were two versions: one without and one with 512K sample RAM (then named "Pro"). You remember: the aged Ultrasound could not work at all without RAM!
Independent from its version however, you could increase the sample RAM using 2 SIMM's to get up to 8 MB - and so nothing more hindered the compatibility mode.
Some resourceful crafters later found out that the DSP supported up to 16 MB - and soldered two further SIMM holders on the back of the card! In 2014, some hackers found a way to expand the RAM with an adaptor without soldering. Instructions regarding this topic can be found in the Web.
As with the predecessor this card mastered mixing of 32 channels in hardware - now however always on CD level! An addition were effects like echo, reverb, chorus, flanging and fading - but these required installed RAM.
Digital recording and playback of sound data happens with up to 48 KHz.
What some users drove slowly into craziness was the high noise level of first card revesions, which was result of a design mistake of the InterWave chipset.
However, AMD pushed a new version of the chip quite fast, and owners with the previous revisions could exchange their cards gratuitously with Advanced Gravis. Nevertheless, AMD soon lost interest to produce this chip or even to develop it further. Presumably, it was not worthwhile. Annoyingly, however also all cards based on it - consequently also the GUS PnP - were influenced by this.
So Advanced Gravis made a step backwards - equipped the "old" GUS with an SB Pro compatible chip made by ESS, which right away replaced the Crystal CoDec, named the result "Extreme" and threw it on the market. Unfortunately with only minor success. After this relapse, Advanced Gravis gave up the development and production of sound cards - "no more profitable business".
Purchasing it used
This card is not too rare, but often overpriced. Since full GF1 compatibility is not always given, only purchase it if you can get it cheaper than an original GF1 based card, or in case you have no other option.