Which Isomac do you have at home? If it's one of their prosumer models with E61 group like the Tea or Rituale or Mondiale or Zaffiro etc. you DO have preinfusion at home. E61 groups automatically have preinfusion built in to the group design. Preinfusion was one of the main patent features of the Faema E61 group.
I would think a "hard" pre-infusion would be detrimental when you consider that the 3-way solenoid valve would disrupt the coffee bed, should there be even marginal pressure to equalize.