It'll be just like said in the review, and for the capped 507 and WM1AM2. The capped version may be fine for some sensitive headphones, but not for others. I found the capped versions fine with the LCD-X and D9200, but was a bit lacking with the focal clear and arya stealth. Uncapped versions were fine with all the above - for my listening levels that is.
Also, remember that low gain on uncapped versions is more powerful than capped versions. I measured my capped WM1AM2 could only put out 0.2V rms.
You should re-review the Zx707. After today’s firmware update the sound signature has changed significantly, for the worse I’m afraid. The deep punchy bass as you describe in your review is no longer there which is one of the highlights of this device. The vocals also appear a bit muddy.
I've got an uncapped version of the 707, with the firmware update and I don't find the vocals muddy they are clean clear but after using Shanling devices for the last several years, the 707 is first Dap that I've needed to turn on the EQ to give a mild boost to 31, 62, 125, 250 2K, 4K, 8K and 16K to match the musicality of the un EQ'd M6 Pro 21