Update 1: sub is plugged in via the 100hz rca pre-out. I ended up lowering the crossover frequency to about 90hz against my own recommendation. I did have a slight phase issue, but I also have a phase switch for that.

Verdict:
Worked fucking great on Yes, Fragile. Worked less great on Led Zeppelin IV.

I'm not sure it's worth the money. But Fragile on vinyl is kicking right now. Really sounds great.

Just following up here in case anyone else has or is considering the Denon PMA 600ne for vinyl playback.

One major limitation is that the bass control only affects the tone around 100hz as confirmed in the manual.

Increasing bass is often overkill at the wrong frequency when wanting to extenuating the lows of a bass guitar or kick drum. These frequencies are often reduced significantly on vinyl.

Luckily, the subout for the Denon is also centered at 100hz. Nothing over 100hz will come out of the Denon's sub-out.

Setting the sub crossover to max bypasses its internal crossover and ensures the full frequency it receives (up to 100hz) is boosted.

If you only want to boost frequencies up to 80 hz for example (a typical roll-off point on vinyl), setting the crossover to 80hz can unwittingly create a cascading effect as both the Denon and the sub will be filtering the signal. This can cause a dip in some frequencies around the targeted range or even create phase issues.

In my case, as my main speakers can reproduce sound to 30hz, and I only really want to boost the 50-80hz range, using high-level speaker inputs on my sub may be the better way, allowing the full range of frequencies to be sent to the sub and only using the sub's crossover for filtering.

Tl;dr: if you want to use the dedicated sub-out on the Denon PMA 600ne to boost the low end (below 100 hz) of your vinyl you should either set the crossover on your sub to bypass (or we'll above 100hz) or use a sub with high-level speaker inputs and set the crossover to a specific range (like 80hz).

I'll update again when my sub gets here. 🤣

Peter Gabriel is on the platter. Watch out.

Morning routine: Make coffee. Pet cat. Start day.

GM. Coffee time. ☕️