"Is the HD 660S2 worth the upgrade from the HD 600?"

"For most listeners: not immediately. The HD 660S2 offers deeper sub-bass extension, a slightly more refined treble, and marginally better imaging. But it costs roughly $200–$250 more than the HD 600. The differences are real but subtle — you need quality amplification and familiar source material to hear them reliably. If you already own the HD 600 and are satisfied, there's no urgent reason to upgrade. If you're choosing between them for a first purchase and budget permits, the HD 660S2 is technically the more complete headphone."

"Does the HD 660S2 need a better amp than the HD 600?"

"Both are 300Ω headphones, but the HD 660S2 is more sensitive (104dB/mW vs 97dB/mW for the HD 600), making it easier to drive to adequate volume. However, the HD 660S2's improved low-frequency extension benefits significantly from a high-current amplifier. A Schiit Asgard 3 or JDS Labs Element III is ideal for the HD 660S2. The HD 600 performs excellently from a Magni Heresy."

"What is the main difference between HD 600 and HD 660S2?"

"The HD 660S2 was designed to address the HD 600's biggest weakness: sub-bass extension. Below 50Hz, the HD 600 rolls off noticeably — the HD 660S2 extends deeper and with more authority. The HD 660S2 also has a slightly smoother treble, making it more forgiving on bright recordings. The HD 600 retains an edge in upper-midrange clarity and remains the more cost-effective reference tool."

Sennheiser HD 600 vs HD 660S2: Is the Upgrade Worth It?

Sennheiser HD 600 vs HD 660S2 — sound differences, amp requirements, price gap analysis, and an honest answer on whether the HD 660S2 justifies its premium.

The Question

The HD 600 costs around $269. The HD 660S2 costs around $499. That’s a $230 gap for two headphones built around a very similar philosophy. Is the upgrade worth it?

Short answer: The HD 660S2 is a better headphone, but the HD 600 remains extraordinary value.

Specs Comparison

	Sennheiser HD 600	Sennheiser HD 660S2
Impedance	300Ω	300Ω
Sensitivity	97 dB/mW	104 dB/mW
Frequency response	12–39,000 Hz	6–41,000 Hz
THD	<0.1%	<0.04%
Weight	260g	260g
Cable	Detachable, dual-sided	Detachable, dual-sided (balanced included)
Typical street price	~$269	~$499

The most significant spec difference: the HD 660S2 ships with a balanced cable in addition to the standard 3.5mm cable, enabling connection to balanced amplifier outputs out of the box.

Sound Differences

Sub-Bass Extension

This is the HD 660S2’s primary advancement over the HD 600. The HD 600’s bass rolls off below approximately 50Hz — it reproduces bass guitar clearly but lacks genuine rumble and sub-bass texture. The HD 660S2 extends to around 30Hz with meaningful authority.

For music with significant low-frequency content — electronic, orchestral, organ — this difference is audible and meaningful. For acoustic guitar, vocal jazz, or chamber music, the practical difference is minimal.

Treble

Both headphones have Sennheiser’s characteristic smooth, detailed treble presentation. The HD 600 has a slight graininess or roughness around 6–8kHz that some find adds character; others find it occasionally fatiguing. The HD 660S2’s treble is more refined — the same level of detail retrieval but with slightly less edge on bright recordings.

If you’re sensitive to sibilance or harshness on poorly mastered music, the HD 660S2 is more forgiving.

Midrange

Both are superb. The HD 600 has a slight emphasis around 3kHz that gives vocals a forward, present quality. The HD 660S2’s midrange is slightly more neutral through this region — vocals are natural rather than pushed. This is a matter of preference; many listeners prefer the HD 600’s vocal presentation.

Imaging and Soundstage

The HD 660S2 has marginally better imaging precision. The HD 600’s soundstage is excellent for its price; the HD 660S2 improves on it subtly. These are not night-and-day differences — they require direct A/B comparison to reliably identify.

Source and Amp Requirements

Source	HD 600	HD 660S2
Phone/laptop (no amp)	Underpowered	Audible, mediocre
FiiO E10K (~$50)	Marginal	Adequate
Schiit Magni Heresy ($109)	Excellent	Good
Schiit Asgard 3 ($199)	Excellent	Excellent
JDS Labs Element III ($299)	Excellent	Excellent
Balanced amp output	N/A	Best

The HD 660S2’s higher sensitivity means it reaches adequate volume from weaker sources more easily than the HD 600. But its improved bass extension requires an amplifier with strong current delivery to materialise fully — the Asgard 3 is the recommended minimum for hearing what the HD 660S2 actually offers.

The included balanced cable pairs well with any amplifier featuring balanced XLR or 4.4mm outputs.

Value Analysis

HD 600 path: $269 headphone + $109 Magni Heresy = $378 total. This is one of the best value audiophile rigs available. You will enjoy this setup for years.

HD 660S2 path: $499 headphone + $199 Asgard 3 = $698 total. This is a materially better-sounding setup. Whether it’s $320 better is the question only you can answer based on how much you care about sub-bass extension and treble smoothness.

Who Should Buy Which

Buy the HD 600 if:

Budget is a primary consideration
You listen to music without significant sub-bass content (acoustic, jazz, classical strings, vocal)
You already have a solid-state amp at the Magni Heresy level
You want a proven reference tool that engineers have trusted for decades
You’re entering the audiophile headphone space and want maximum value

Buy the HD 660S2 if:

You listen to music with meaningful low-frequency content and want it reproduced accurately
You have a quality amplifier (Asgard 3 level or better) or are budgeting for one
You want the balanced cable output included
You find the HD 600’s occasional treble edge fatiguing
Budget is not a significant constraint

The HD 600 is not obsolete. It remains among the finest headphones ever made at its price. The HD 660S2 is simply what the HD 600 would be if designed with today’s materials and a higher budget target.