There are a lot of cheaper phono preamps out there. If it sounds great as is, I would leave it as is. There is probably not much to gain from shelling out big bucks for a pre-amp to enhance the Oyster. The law of diminishing returns seems to apply to phono cartridges. I have the Black Pearl and if I were going to get a pre-amp for it I wouldn't spend more than $200 for it. The phono amp in my 990 works just fine for me.
_________________________
Music system
Model 990/7500/Magnepan 1.6 QRs/Technics SL1200 MK2/Aperion S-12 Subwoofer/OWA3/Sony NS75H DVD
APC H15 Power Conditioner

TV System
Large Advent Loudspeakers/ Polk center/Monoprice surrounds/Panasonic Viera 42 inch/Onkyo HT-RC260/Sony BDP S590/Directv


Home Theater System
Onkyo PR-SC886/Outlaw 7125 Klipsch RF-82 L/R,RC-62 center, RB-35 SR/SL, BENQ HT1075, Outlaw LFM1-EX/OPPO BDP-83/Directv
Harmony ONE
Blue Jeans and Monoprice interconnects
APC H15 Power Conditioner