Is the Schiit Magnius up to the task ???

I would put my money on your current single-ended setup being better than inserting an active Schiit component for no good reason. Honestly you’d have to put a gun to my head to get me to insert any Schiit into my analog chain.

If you’re concerned that the Simaudio’s balanced out has some magical sonic properties over SE - it might in fact only be using half its circuitry for SE outputs, in which case the balanced outs *might* sound better (maybe). In that case I’d go for a Jensen ISOMax line-level converter (XLR to RCA) before anything else. I’ve used one of these in the other direction - taking a SE phono stage into a balanced headphone amp - and it sounded great; there was distinct sonic advantage over full SE in that particular case, because that headphone amp only used half its circuitry in SE (note: an amp with differential input stage wouldn't have cared whether SE or balanced).

Somebody else can speak the the potential usefulness of simple XLR - RCA adapters (Cardas makes nice ones) in this application, but both the adapters and the Jensen box are handy to have in your audiophile toolkit :)

Audio by Van Alstine makes a single to balanced converter box that is much higher quality than the converter plugs you can buy.

If the itch is unbearable buy a fully balanced amp like one of Ralph's.

I have the very similar Simaudio LP310 and prefer the XLR out to Pass preamp...and also agree XLR often simply provides more solid connection...I would keep the Magnius away from the Sim

Paul McGowan enlightened me about the benefits of XLR some 25 years ago, BUT, the I/Os must be TRUE balanced circuits to enjoy what XLR is capable of.

As to only good for long runs: I compared the exact same manufacturer same run of 0.5m to1.0m XLRs and easily heard the differences

hth