I noticed the same: the bass is more prominent, and the sound opens up quite a bit, which can be perceived as a larger soundstage. The differences are all but marginal. Obviously, the amount of alteration, especially the soundstage one, is strictly DAC-related, but this only affects the "amount" of it; the change itself happens regardless.
To further verify the alterations in sound between PO and BAL, I ended up using all my (three models: Red Chain, T2 Pro, and T3 Pro) TRN modular cables so that I could have a stable variable when comparing 3.5mm vs. 4.4mm.
At the end of the day, with all three cables—let aside the unique differences they each apport to sound because of different impedances and materials used—the increase in bass and perceived soundstage was a constant when switching from PO to BAL for all of them.
In this regard, I would like to add that, compared to some time ago, I don't consider BAL the inherently "superior" experience anymore. I'm starting to think they both have their merits. For example, in PO, among many other things, the sound tends to sound more crispy and "concentrated" than it does in BAL; also, the added bass in BAL does not always mean a better experience, especially with already bassy IEMs. Anyway, I think both are good in their own way and also different enough to be both worth experiencing.
And that's one of the main reasons why lately I've been buying only TRN modular cables. I think their versatility is well worth the investment, they sound very good, they are quite comfortable, and their price is extremely competitive too. (Also, I don't know any other companies that produce such good modular cables at this price; if someone has any recommendations, I'd very grateful!).