Please recommend a PreAmp for my 5.1 home theatre system

on paper it looks ok... but ask Oppo and they'll tell you for best results, its better to use a preamp for the volume control...... know that all volume controls does some harm to the signal.. its just that some does less harm than others.. analog seems to work the best thats why you see higher end preamps/processors incorporate an analog volume control into their all digital preamps.. My Classe SSP800 has an analog volume control for example..  there's many different designs in volume control, each one trying to better the other.. PS Audio claims they make the best one yet

Another vote for the Anthem AVM 60. Nice unit for both h/t and 2 channel.

Oppo: https://www.oppodigital.com.au/blogs/reviews-resources/15420449-using-your-oppo-as-a-pre-amplifier
For digital vs analogue volume control, I simply repeat the reference to the Sabre presentation (there is also a longer text by Sabre but I could not quickly find it). Can you hear imperfections at -135dB, and do you have source material that is this clean? Do not forget that analogue volume controls have their weakneses as well, like channel imbalance at lower levels. There are more important things to worry about.

Hi, I also have the Focal Sopra 2, Focal Chorus surrounds and am waiting for the Focal Sopra Center to arrive this week. I am using Marantz 8801 as a preamp/pocessor and am extremely happy with it.
I have tried using the Oppo 95 as a preamp before buying the Marantz and the Focals, but the sound was horrible so I would definitely recommend using a real processor.