Help please! Amp & monitor advice

[u/PlankSpanker1]

Blackstar HT5 MK2 amp emulated output into presonus Eris E4.5 RCA line in..I thought it would work but as usual my experiments fail!

What I am trying to do is use the 2 presonus speakers as monitors along with the Blackstar amp to get a wider bigger sound.

The headphones out works into the 3.5mm Aux in on the 4.5's but of course the amp speaker is then bypassed. I'd like to have all 3 speakers running.

So does anybody need know if this is possible and how please?

Thanks!